def legalize_integer_nearest(optree): """ transform a NearestInteger node floating-point to integer into a sequence of floating-point NearestInteger and Conversion. This conversion is lossy """ op_input = optree.get_input(0) int_precision = { v4float32: v4int32, ML_Binary32: ML_Int32 }[optree.get_precision()] return Conversion(NearestInteger(op_input, precision=int_precision), precision=optree.get_precision())
def generate_scheme(self): # declaring target and instantiating optimization engine vx = self.implementation.add_input_variable("x", self.precision) Log.set_dump_stdout(True) Log.report(Log.Info, "\033[33;1m generating implementation scheme \033[0m") if self.debug_flag: Log.report(Log.Info, "\033[31;1m debug has been enabled \033[0;m") # local overloading of RaiseReturn operation def ExpRaiseReturn(*args, **kwords): kwords["arg_value"] = vx kwords["function_name"] = self.function_name if self.libm_compliant: return RaiseReturn(*args, precision=self.precision, **kwords) else: return Return(kwords["return_value"], precision=self.precision) test_nan_or_inf = Test(vx, specifier=Test.IsInfOrNaN, likely=False, debug=debug_multi, tag="nan_or_inf") test_nan = Test(vx, specifier=Test.IsNaN, debug=debug_multi, tag="is_nan_test") test_positive = Comparison(vx, 0, specifier=Comparison.GreaterOrEqual, debug=debug_multi, tag="inf_sign") test_signaling_nan = Test(vx, specifier=Test.IsSignalingNaN, debug=debug_multi, tag="is_signaling_nan") return_snan = Statement( ExpRaiseReturn(ML_FPE_Invalid, return_value=FP_QNaN(self.precision))) # return in case of infinity input infty_return = Statement( ConditionBlock( test_positive, Return(FP_PlusInfty(self.precision), precision=self.precision), Return(FP_PlusZero(self.precision), precision=self.precision))) # return in case of specific value input (NaN or inf) specific_return = ConditionBlock( test_nan, ConditionBlock( test_signaling_nan, return_snan, Return(FP_QNaN(self.precision), precision=self.precision)), infty_return) # return in case of standard (non-special) input # exclusion of early overflow and underflow cases precision_emax = self.precision.get_emax() precision_max_value = S2 * S2**precision_emax exp_overflow_bound = sollya.ceil(log(precision_max_value)) early_overflow_test = Comparison(vx, exp_overflow_bound, likely=False, specifier=Comparison.Greater) early_overflow_return = Statement( ClearException() if self.libm_compliant else Statement(), ExpRaiseReturn(ML_FPE_Inexact, ML_FPE_Overflow, return_value=FP_PlusInfty(self.precision))) precision_emin = self.precision.get_emin_subnormal() precision_min_value = S2**precision_emin exp_underflow_bound = floor(log(precision_min_value)) early_underflow_test = Comparison(vx, exp_underflow_bound, likely=False, specifier=Comparison.Less) early_underflow_return = Statement( ClearException() if self.libm_compliant else Statement(), ExpRaiseReturn(ML_FPE_Inexact, ML_FPE_Underflow, return_value=FP_PlusZero(self.precision))) # constant computation invlog2 = self.precision.round_sollya_object(1 / log(2), sollya.RN) interval_vx = Interval(exp_underflow_bound, exp_overflow_bound) interval_fk = interval_vx * invlog2 interval_k = Interval(floor(inf(interval_fk)), sollya.ceil(sup(interval_fk))) log2_hi_precision = self.precision.get_field_size() - ( sollya.ceil(log2(sup(abs(interval_k)))) + 2) Log.report(Log.Info, "log2_hi_precision: %d" % log2_hi_precision) invlog2_cst = Constant(invlog2, precision=self.precision) log2_hi = round(log(2), log2_hi_precision, sollya.RN) log2_lo = self.precision.round_sollya_object( log(2) - log2_hi, sollya.RN) # argument reduction unround_k = vx * invlog2 unround_k.set_attributes(tag="unround_k", debug=debug_multi) k = NearestInteger(unround_k, precision=self.precision, debug=debug_multi) ik = NearestInteger(unround_k, precision=self.precision.get_integer_format(), debug=debug_multi, tag="ik") ik.set_tag("ik") k.set_tag("k") exact_pre_mul = (k * log2_hi) exact_pre_mul.set_attributes(exact=True) exact_hi_part = vx - exact_pre_mul exact_hi_part.set_attributes(exact=True, tag="exact_hi", debug=debug_multi, prevent_optimization=True) exact_lo_part = -k * log2_lo exact_lo_part.set_attributes(tag="exact_lo", debug=debug_multi, prevent_optimization=True) r = exact_hi_part + exact_lo_part r.set_tag("r") r.set_attributes(debug=debug_multi) approx_interval = Interval(-log(2) / 2, log(2) / 2) approx_interval_half = approx_interval / 2 approx_interval_split = [ Interval(-log(2) / 2, inf(approx_interval_half)), approx_interval_half, Interval(sup(approx_interval_half), log(2) / 2) ] # TODO: should be computed automatically exact_hi_interval = approx_interval exact_lo_interval = -interval_k * log2_lo opt_r = self.optimise_scheme(r, copy={}) tag_map = {} self.opt_engine.register_nodes_by_tag(opt_r, tag_map) cg_eval_error_copy_map = { vx: Variable("x", precision=self.precision, interval=interval_vx), tag_map["k"]: Variable("k", interval=interval_k, precision=self.precision) } #try: if is_gappa_installed(): eval_error = self.gappa_engine.get_eval_error_v2( self.opt_engine, opt_r, cg_eval_error_copy_map, gappa_filename="red_arg.g") else: eval_error = 0.0 Log.report(Log.Warning, "gappa is not installed in this environnement") Log.report(Log.Info, "eval error: %s" % eval_error) local_ulp = sup(ulp(sollya.exp(approx_interval), self.precision)) # FIXME refactor error_goal from accuracy Log.report(Log.Info, "accuracy: %s" % self.accuracy) if isinstance(self.accuracy, ML_Faithful): error_goal = local_ulp elif isinstance(self.accuracy, ML_CorrectlyRounded): error_goal = S2**-1 * local_ulp elif isinstance(self.accuracy, ML_DegradedAccuracyAbsolute): error_goal = self.accuracy.goal elif isinstance(self.accuracy, ML_DegradedAccuracyRelative): error_goal = self.accuracy.goal else: Log.report(Log.Error, "unknown accuracy: %s" % self.accuracy) # error_goal = local_ulp #S2**-(self.precision.get_field_size()+1) error_goal_approx = S2**-1 * error_goal Log.report(Log.Info, "\033[33;1m building mathematical polynomial \033[0m\n") poly_degree = max( sup( guessdegree( expm1(sollya.x) / sollya.x, approx_interval, error_goal_approx)) - 1, 2) init_poly_degree = poly_degree error_function = lambda p, f, ai, mod, t: dirtyinfnorm(f - p, ai) polynomial_scheme_builder = PolynomialSchemeEvaluator.generate_estrin_scheme #polynomial_scheme_builder = PolynomialSchemeEvaluator.generate_horner_scheme while 1: Log.report(Log.Info, "attempting poly degree: %d" % poly_degree) precision_list = [1] + [self.precision] * (poly_degree) poly_object, poly_approx_error = Polynomial.build_from_approximation_with_error( expm1(sollya.x), poly_degree, precision_list, approx_interval, sollya.absolute, error_function=error_function) Log.report(Log.Info, "polynomial: %s " % poly_object) sub_poly = poly_object.sub_poly(start_index=2) Log.report(Log.Info, "polynomial: %s " % sub_poly) Log.report(Log.Info, "poly approx error: %s" % poly_approx_error) Log.report( Log.Info, "\033[33;1m generating polynomial evaluation scheme \033[0m") pre_poly = polynomial_scheme_builder( poly_object, r, unified_precision=self.precision) pre_poly.set_attributes(tag="pre_poly", debug=debug_multi) pre_sub_poly = polynomial_scheme_builder( sub_poly, r, unified_precision=self.precision) pre_sub_poly.set_attributes(tag="pre_sub_poly", debug=debug_multi) poly = 1 + (exact_hi_part + (exact_lo_part + pre_sub_poly)) poly.set_tag("poly") # optimizing poly before evaluation error computation #opt_poly = self.opt_engine.optimization_process(poly, self.precision, fuse_fma = fuse_fma) #opt_sub_poly = self.opt_engine.optimization_process(pre_sub_poly, self.precision, fuse_fma = fuse_fma) opt_poly = self.optimise_scheme(poly) opt_sub_poly = self.optimise_scheme(pre_sub_poly) # evaluating error of the polynomial approximation r_gappa_var = Variable("r", precision=self.precision, interval=approx_interval) exact_hi_gappa_var = Variable("exact_hi", precision=self.precision, interval=exact_hi_interval) exact_lo_gappa_var = Variable("exact_lo", precision=self.precision, interval=exact_lo_interval) vx_gappa_var = Variable("x", precision=self.precision, interval=interval_vx) k_gappa_var = Variable("k", interval=interval_k, precision=self.precision) #print "exact_hi interval: ", exact_hi_interval sub_poly_error_copy_map = { #r.get_handle().get_node(): r_gappa_var, #vx.get_handle().get_node(): vx_gappa_var, exact_hi_part.get_handle().get_node(): exact_hi_gappa_var, exact_lo_part.get_handle().get_node(): exact_lo_gappa_var, #k.get_handle().get_node(): k_gappa_var, } poly_error_copy_map = { exact_hi_part.get_handle().get_node(): exact_hi_gappa_var, exact_lo_part.get_handle().get_node(): exact_lo_gappa_var, } if is_gappa_installed(): sub_poly_eval_error = -1.0 sub_poly_eval_error = self.gappa_engine.get_eval_error_v2( self.opt_engine, opt_sub_poly, sub_poly_error_copy_map, gappa_filename="%s_gappa_sub_poly.g" % self.function_name) dichotomy_map = [ { exact_hi_part.get_handle().get_node(): approx_interval_split[0], }, { exact_hi_part.get_handle().get_node(): approx_interval_split[1], }, { exact_hi_part.get_handle().get_node(): approx_interval_split[2], }, ] poly_eval_error_dico = self.gappa_engine.get_eval_error_v3( self.opt_engine, opt_poly, poly_error_copy_map, gappa_filename="gappa_poly.g", dichotomy=dichotomy_map) poly_eval_error = max( [sup(abs(err)) for err in poly_eval_error_dico]) else: poly_eval_error = 0.0 sub_poly_eval_error = 0.0 Log.report(Log.Warning, "gappa is not installed in this environnement") Log.report(Log.Info, "stopping autonomous degree research") # incrementing polynomial degree to counteract initial decrementation effect poly_degree += 1 break Log.report(Log.Info, "poly evaluation error: %s" % poly_eval_error) Log.report(Log.Info, "sub poly evaluation error: %s" % sub_poly_eval_error) global_poly_error = None global_rel_poly_error = None for case_index in range(3): poly_error = poly_approx_error + poly_eval_error_dico[ case_index] rel_poly_error = sup( abs(poly_error / sollya.exp(approx_interval_split[case_index]))) if global_rel_poly_error == None or rel_poly_error > global_rel_poly_error: global_rel_poly_error = rel_poly_error global_poly_error = poly_error flag = error_goal > global_rel_poly_error if flag: break else: poly_degree += 1 late_overflow_test = Comparison(ik, self.precision.get_emax(), specifier=Comparison.Greater, likely=False, debug=debug_multi, tag="late_overflow_test") overflow_exp_offset = (self.precision.get_emax() - self.precision.get_field_size() / 2) diff_k = Subtraction( ik, Constant(overflow_exp_offset, precision=self.precision.get_integer_format()), precision=self.precision.get_integer_format(), debug=debug_multi, tag="diff_k", ) late_overflow_result = (ExponentInsertion( diff_k, precision=self.precision) * poly) * ExponentInsertion( overflow_exp_offset, precision=self.precision) late_overflow_result.set_attributes(silent=False, tag="late_overflow_result", debug=debug_multi, precision=self.precision) late_overflow_return = ConditionBlock( Test(late_overflow_result, specifier=Test.IsInfty, likely=False), ExpRaiseReturn(ML_FPE_Overflow, return_value=FP_PlusInfty(self.precision)), Return(late_overflow_result, precision=self.precision)) late_underflow_test = Comparison(k, self.precision.get_emin_normal(), specifier=Comparison.LessOrEqual, likely=False) underflow_exp_offset = 2 * self.precision.get_field_size() corrected_exp = Addition( ik, Constant(underflow_exp_offset, precision=self.precision.get_integer_format()), precision=self.precision.get_integer_format(), tag="corrected_exp") late_underflow_result = ( ExponentInsertion(corrected_exp, precision=self.precision) * poly) * ExponentInsertion(-underflow_exp_offset, precision=self.precision) late_underflow_result.set_attributes(debug=debug_multi, tag="late_underflow_result", silent=False) test_subnormal = Test(late_underflow_result, specifier=Test.IsSubnormal) late_underflow_return = Statement( ConditionBlock( test_subnormal, ExpRaiseReturn(ML_FPE_Underflow, return_value=late_underflow_result)), Return(late_underflow_result, precision=self.precision)) twok = ExponentInsertion(ik, tag="exp_ik", debug=debug_multi, precision=self.precision) #std_result = twok * ((1 + exact_hi_part * pre_poly) + exact_lo_part * pre_poly) std_result = twok * poly std_result.set_attributes(tag="std_result", debug=debug_multi) result_scheme = ConditionBlock( late_overflow_test, late_overflow_return, ConditionBlock(late_underflow_test, late_underflow_return, Return(std_result, precision=self.precision))) std_return = ConditionBlock( early_overflow_test, early_overflow_return, ConditionBlock(early_underflow_test, early_underflow_return, result_scheme)) # main scheme Log.report(Log.Info, "\033[33;1m MDL scheme \033[0m") scheme = ConditionBlock( test_nan_or_inf, Statement(ClearException() if self.libm_compliant else Statement(), specific_return), std_return) return scheme
def piecewise_approximation(function, variable, precision, bound_low=-1.0, bound_high=1.0, num_intervals=16, max_degree=2, error_threshold=S2**-24, odd=False, even=False): """ Generate a piecewise approximation :param function: function to be approximated :type function: SollyaObject :param variable: input variable :type variable: Variable :param precision: variable's format :type precision: ML_Format :param bound_low: lower bound for the approximation interval :param bound_high: upper bound for the approximation interval :param num_intervals: number of sub-interval / sub-division of the main interval :param max_degree: maximum degree for an approximation on any sub-interval :param error_threshold: error bound for an approximation on any sub-interval :return: pair (scheme, error) where scheme is a graph node for an approximation scheme of function evaluated at variable, and error is the maximum approximation error encountered :rtype tuple(ML_Operation, SollyaObject): """ degree_generator = piecewise_approximation_degree_generator( function, bound_low, bound_high, num_intervals=num_intervals, error_threshold=error_threshold, ) degree_list = list(degree_generator) # if max_degree is None then we determine it locally if max_degree is None: max_degree = max(degree_list) # table to store coefficients of the approximation on each segment coeff_table = ML_NewTable( dimensions=[num_intervals, max_degree + 1], storage_precision=precision, tag="coeff_table", const=True # by default all approximation coeff table are const ) error_function = lambda p, f, ai, mod, t: sollya.dirtyinfnorm(p - f, ai) max_approx_error = 0.0 interval_size = (bound_high - bound_low) / num_intervals for i in range(num_intervals): subint_low = bound_low + i * interval_size subint_high = bound_low + (i + 1) * interval_size local_function = function(sollya.x + subint_low) local_interval = Interval(-interval_size, interval_size) local_degree = degree_list[i] if local_degree > max_degree: Log.report( Log.Warning, "local_degree {} exceeds max_degree bound ({}) in piecewise_approximation", local_degree, max_degree) # as max_degree defines the size of the table we can use # it as the degree for each sub-interval polynomial # as there is nothing to gain (yet) by using a smaller polynomial degree = max_degree # min(max_degree, local_degree) if function(subint_low) == 0.0: # if the lower bound is a zero to the function, we # need to force value=0 for the constant coefficient # and extend the approximation interval local_poly_degree_list = list( range(1 if even else 0, degree + 1, 2 if odd or even else 1)) poly_object, approx_error = Polynomial.build_from_approximation_with_error( function(sollya.x) / sollya.x, local_poly_degree_list, [precision] * len(local_poly_degree_list), Interval(-subint_high * 0.95, subint_high), sollya.absolute, error_function=error_function) # multiply by sollya.x poly_object = poly_object.sub_poly(offset=-1) else: try: poly_object, approx_error = Polynomial.build_from_approximation_with_error( local_function, degree, [precision] * (degree + 1), local_interval, sollya.absolute, error_function=error_function) except SollyaError as err: # try to see if function is constant on the interval (possible # failure cause for fpminmax) cst_value = precision.round_sollya_object( function(subint_low), sollya.RN) accuracy = error_threshold diff_with_cst_range = sollya.supnorm(cst_value, local_function, local_interval, sollya.absolute, accuracy) diff_with_cst = sup(abs(diff_with_cst_range)) if diff_with_cst < error_threshold: Log.report(Log.Info, "constant polynomial detected") poly_object = Polynomial([function(subint_low)] + [0] * degree) approx_error = diff_with_cst else: Log.report( Log.error, "degree: {} for index {}, diff_with_cst={} (vs error_threshold={}) ", degree, i, diff_with_cst, error_threshold, error=err) for ci in range(max_degree + 1): if ci in poly_object.coeff_map: coeff_table[i][ci] = poly_object.coeff_map[ci] else: coeff_table[i][ci] = 0.0 if approx_error > error_threshold: Log.report( Log.Warning, "piecewise_approximation on index {} exceeds error threshold: {} > {}", i, approx_error, error_threshold) max_approx_error = max(max_approx_error, abs(approx_error)) # computing offset diff = Subtraction(variable, Constant(bound_low, precision=precision), tag="diff", debug=debug_multi, precision=precision) int_prec = precision.get_integer_format() # delta = bound_high - bound_low delta_ratio = Constant(num_intervals / (bound_high - bound_low), precision=precision) # computing table index # index = nearestint(diff / delta * <num_intervals>) index = Max(0, Min( NearestInteger( Multiplication(diff, delta_ratio, precision=precision), precision=int_prec, ), num_intervals - 1), tag="index", debug=debug_multi, precision=int_prec) poly_var = Subtraction(diff, Multiplication( Conversion(index, precision=precision), Constant(interval_size, precision=precision)), precision=precision, tag="poly_var", debug=debug_multi) # generating indexed polynomial coeffs = [(ci, TableLoad(coeff_table, index, ci)) for ci in range(max_degree + 1)][::-1] poly_scheme = PolynomialSchemeEvaluator.generate_horner_scheme2( coeffs, poly_var, precision, {}, precision) return poly_scheme, max_approx_error
def generate_scalar_scheme(self, vx, vy): # fixing inputs' node tag vx.set_attributes(tag="x") vy.set_attributes(tag="y") int_precision = self.precision.get_integer_format() # assuming x = m.2^e (m in [1, 2[) # n, positive or null integers # # pow(x, n) = x^(y) # = exp(y * log(x)) # = 2^(y * log2(x)) # = 2^(y * (log2(m) + e)) # e = ExponentExtraction(vx, tag="e", precision=int_precision) m = MantissaExtraction(vx, tag="m", precision=self.precision) # approximation log2(m) # retrieving processor inverse approximation table dummy_var = Variable("dummy", precision = self.precision) dummy_div_seed = ReciprocalSeed(dummy_var, precision = self.precision) inv_approx_table = self.processor.get_recursive_implementation( dummy_div_seed, language=None, table_getter= lambda self: self.approx_table_map) log_f = sollya.log(sollya.x) # /sollya.log(self.basis) ml_log_args = ML_GenericLog.get_default_args(precision=self.precision, basis=2) ml_log = ML_GenericLog(ml_log_args) log_table, log_table_tho, table_index_range = ml_log.generate_log_table(log_f, inv_approx_table) log_approx = ml_log.generate_reduced_log_split(Abs(m, precision=self.precision), log_f, inv_approx_table, log_table) log_approx = Select(Equal(vx, 0), FP_MinusInfty(self.precision), log_approx) log_approx.set_attributes(tag="log_approx", debug=debug_multi) r = Multiplication(log_approx, vy, tag="r", debug=debug_multi) # 2^(y * (log2(m) + e)) = 2^(y * log2(m)) * 2^(y * e) # # log_approx = log2(Abs(m)) # r = y * log_approx ~ y * log2(m) # # NOTES: manage cases where e is negative and # (y * log2(m)) AND (y * e) could cancel out # if e positive, whichever the sign of y (y * log2(m)) and (y * e) CANNOT # be of opposite signs # log2(m) in [0, 1[ so cancellation can occur only if e == -1 # we split 2^x in 2^x = 2^t0 * 2^t1 # if e < 0: t0 = y * (log2(m) + e), t1=0 # else: t0 = y * log2(m), t1 = y * e t_cond = e < 0 # e_y ~ e * y e_f = Conversion(e, precision=self.precision) #t0 = Select(t_cond, (e_f + log_approx) * vy, Multiplication(e_f, vy), tag="t0") #NearestInteger(t0, precision=self.precision, tag="t0_int") EY = NearestInteger(e_f * vy, tag="EY", precision=self.precision) LY = NearestInteger(log_approx * vy, tag="LY", precision=self.precision) t0_int = Select(t_cond, EY + LY, EY, tag="t0_int") t0_frac = Select(t_cond, FMA(e_f, vy, -EY) + FMA(log_approx, vy, -LY) ,EY - t0_int, tag="t0_frac") #t0_frac.set_attributes(tag="t0_frac") ml_exp2_args = ML_Exp2.get_default_args(precision=self.precision) ml_exp2 = ML_Exp2(ml_exp2_args) exp2_t0_frac = ml_exp2.generate_scalar_scheme(t0_frac, inline_select=True) exp2_t0_frac.set_attributes(tag="exp2_t0_frac", debug=debug_multi) exp2_t0_int = ExponentInsertion(Conversion(t0_int, precision=int_precision), precision=self.precision, tag="exp2_t0_int") t1 = Select(t_cond, Constant(0, precision=self.precision), r) exp2_t1 = ml_exp2.generate_scalar_scheme(t1, inline_select=True) exp2_t1.set_attributes(tag="exp2_t1", debug=debug_multi) result_sign = Constant(1.0, precision=self.precision) # Select(n_is_odd, CopySign(vx, Constant(1.0, precision=self.precision)), 1) y_int = NearestInteger(vy, precision=self.precision) y_is_integer = Equal(y_int, vy) y_is_even = LogicalOr( # if y is a number (exc. inf) greater than 2**mantissa_size * 2, # then it is an integer multiple of 2 => even Abs(vy) >= 2**(self.precision.get_mantissa_size()+1), LogicalAnd( y_is_integer and Abs(vy) < 2**(self.precision.get_mantissa_size()+1), # we want to limit the modulo computation to an integer input Equal(Modulo(Conversion(y_int, precision=int_precision), 2), 0) ) ) y_is_odd = LogicalAnd( LogicalAnd( Abs(vy) < 2**(self.precision.get_mantissa_size()+1), y_is_integer ), Equal(Modulo(Conversion(y_int, precision=int_precision), 2), 1) ) # special cases management special_case_results = Statement( # x is sNaN OR y is sNaN ConditionBlock( LogicalOr(Test(vx, specifier=Test.IsSignalingNaN), Test(vy, specifier=Test.IsSignalingNaN)), Return(FP_QNaN(self.precision)) ), # pow(x, ±0) is 1 if x is not a signaling NaN ConditionBlock( Test(vy, specifier=Test.IsZero), Return(Constant(1.0, precision=self.precision)) ), # pow(±0, y) is ±∞ and signals the divideByZero exception for y an odd integer <0 ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsZero), LogicalAnd(y_is_odd, vy < 0)), Return(Select(Test(vx, specifier=Test.IsPositiveZero), FP_PlusInfty(self.precision), FP_MinusInfty(self.precision))), ), # pow(±0, −∞) is +∞ with no exception ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsZero), Test(vy, specifier=Test.IsNegativeInfty)), Return(FP_MinusInfty(self.precision)), ), # pow(±0, +∞) is +0 with no exception ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsZero), Test(vy, specifier=Test.IsPositiveInfty)), Return(FP_PlusInfty(self.precision)), ), # pow(±0, y) is ±0 for finite y>0 an odd integer ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsZero), LogicalAnd(y_is_odd, vy > 0)), Return(vx), ), # pow(−1, ±∞) is 1 with no exception ConditionBlock( LogicalAnd(Equal(vx, -1), Test(vy, specifier=Test.IsInfty)), Return(Constant(1.0, precision=self.precision)), ), # pow(+1, y) is 1 for any y (even a quiet NaN) ConditionBlock( vx == 1, Return(Constant(1.0, precision=self.precision)), ), # pow(x, +∞) is +0 for −1<x<1 ConditionBlock( LogicalAnd(Abs(vx) < 1, Test(vy, specifier=Test.IsPositiveInfty)), Return(FP_PlusZero(self.precision)) ), # pow(x, +∞) is +∞ for x<−1 or for 1<x (including ±∞) ConditionBlock( LogicalAnd(Abs(vx) > 1, Test(vy, specifier=Test.IsPositiveInfty)), Return(FP_PlusInfty(self.precision)) ), # pow(x, −∞) is +∞ for −1<x<1 ConditionBlock( LogicalAnd(Abs(vx) < 1, Test(vy, specifier=Test.IsNegativeInfty)), Return(FP_PlusInfty(self.precision)) ), # pow(x, −∞) is +0 for x<−1 or for 1<x (including ±∞) ConditionBlock( LogicalAnd(Abs(vx) > 1, Test(vy, specifier=Test.IsNegativeInfty)), Return(FP_PlusZero(self.precision)) ), # pow(+∞, y) is +0 for a number y < 0 ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsPositiveInfty), vy < 0), Return(FP_PlusZero(self.precision)) ), # pow(+∞, y) is +∞ for a number y > 0 ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsPositiveInfty), vy > 0), Return(FP_PlusInfty(self.precision)) ), # pow(−∞, y) is −0 for finite y < 0 an odd integer # TODO: check y is finite ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsNegativeInfty), LogicalAnd(y_is_odd, vy < 0)), Return(FP_MinusZero(self.precision)), ), # pow(−∞, y) is −∞ for finite y > 0 an odd integer # TODO: check y is finite ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsNegativeInfty), LogicalAnd(y_is_odd, vy > 0)), Return(FP_MinusInfty(self.precision)), ), # pow(−∞, y) is +0 for finite y < 0 and not an odd integer # TODO: check y is finite ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsNegativeInfty), LogicalAnd(LogicalNot(y_is_odd), vy < 0)), Return(FP_PlusZero(self.precision)), ), # pow(−∞, y) is +∞ for finite y > 0 and not an odd integer # TODO: check y is finite ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsNegativeInfty), LogicalAnd(LogicalNot(y_is_odd), vy > 0)), Return(FP_PlusInfty(self.precision)), ), # pow(±0, y) is +∞ and signals the divideByZero exception for finite y<0 and not an odd integer # TODO: signal divideByZero exception ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsZero), LogicalAnd(LogicalNot(y_is_odd), vy < 0)), Return(FP_PlusInfty(self.precision)), ), # pow(±0, y) is +0 for finite y>0 and not an odd integer ConditionBlock( LogicalAnd(Test(vx, specifier=Test.IsZero), LogicalAnd(LogicalNot(y_is_odd), vy > 0)), Return(FP_PlusZero(self.precision)), ), ) # manage n=1 separately to avoid catastrophic propagation of errors # between log2 and exp2 to eventually compute the identity function # test-case #3 result = Statement( special_case_results, # fallback default cases Return(result_sign * exp2_t1 * exp2_t0_int * exp2_t0_frac)) return result
def generate_scalar_scheme(self, vx, n): # fixing inputs' node tag vx.set_attributes(tag="x") n.set_attributes(tag="n") int_precision = self.precision.get_integer_format() # assuming x = m.2^e (m in [1, 2[) # n, positive or null integers # # rootn(x, n) = x^(1/n) # = exp(1/n * log(x)) # = 2^(1/n * log2(x)) # = 2^(1/n * (log2(m) + e)) # # approximation log2(m) # retrieving processor inverse approximation table dummy_var = Variable("dummy", precision=self.precision) dummy_div_seed = ReciprocalSeed(dummy_var, precision=self.precision) inv_approx_table = self.processor.get_recursive_implementation( dummy_div_seed, language=None, table_getter=lambda self: self.approx_table_map) log_f = sollya.log(sollya.x) # /sollya.log(self.basis) use_reciprocal = False # non-scaled vx used to compute vx^1 unmodified_vx = vx is_subnormal = Test(vx, specifier=Test.IsSubnormal, tag="is_subnormal") exp_correction_factor = self.precision.get_mantissa_size() mantissa_factor = Constant(2**exp_correction_factor, tag="mantissa_factor") vx = Select(is_subnormal, vx * mantissa_factor, vx, tag="corrected_vx") m = MantissaExtraction(vx, tag="m", precision=self.precision) e = ExponentExtraction(vx, tag="e", precision=int_precision) e = Select(is_subnormal, e - exp_correction_factor, e, tag="corrected_e") ml_log_args = ML_GenericLog.get_default_args(precision=self.precision, basis=2) ml_log = ML_GenericLog(ml_log_args) log_table, log_table_tho, table_index_range = ml_log.generate_log_table( log_f, inv_approx_table) log_approx = ml_log.generate_reduced_log_split( Abs(m, precision=self.precision), log_f, inv_approx_table, log_table) # floating-point version of n n_f = Conversion(n, precision=self.precision, tag="n_f") inv_n = Division(Constant(1, precision=self.precision), n_f) log_approx = Select(Equal(vx, 0), FP_MinusInfty(self.precision), log_approx) log_approx.set_attributes(tag="log_approx", debug=debug_multi) if use_reciprocal: r = Multiplication(log_approx, inv_n, tag="r", debug=debug_multi) else: r = Division(log_approx, n_f, tag="r", debug=debug_multi) # e_n ~ e / n e_f = Conversion(e, precision=self.precision, tag="e_f") if use_reciprocal: e_n = Multiplication(e_f, inv_n, tag="e_n") else: e_n = Division(e_f, n_f, tag="e_n") error_e_n = FMA(e_n, -n_f, e_f, tag="error_e_n") e_n_int = NearestInteger(e_n, precision=self.precision, tag="e_n_int") pre_e_n_frac = e_n - e_n_int pre_e_n_frac.set_attributes(tag="pre_e_n_frac") e_n_frac = pre_e_n_frac + error_e_n * inv_n e_n_frac.set_attributes(tag="e_n_frac") ml_exp2_args = ML_Exp2.get_default_args(precision=self.precision) ml_exp2 = ML_Exp2(ml_exp2_args) exp2_r = ml_exp2.generate_scalar_scheme(r, inline_select=True) exp2_r.set_attributes(tag="exp2_r", debug=debug_multi) exp2_e_n_frac = ml_exp2.generate_scalar_scheme(e_n_frac, inline_select=True) exp2_e_n_frac.set_attributes(tag="exp2_e_n_frac", debug=debug_multi) exp2_e_n_int = ExponentInsertion(Conversion(e_n_int, precision=int_precision), precision=self.precision, tag="exp2_e_n_int") n_is_even = Equal(Modulo(n, 2), 0, tag="n_is_even", debug=debug_multi) n_is_odd = LogicalNot(n_is_even, tag="n_is_odd") result_sign = Select( n_is_odd, CopySign(vx, Constant(1.0, precision=self.precision)), 1) # managing n == -1 if self.expand_div: ml_division_args = ML_Division.get_default_args( precision=self.precision, input_formats=[self.precision] * 2) ml_division = ML_Division(ml_division_args) self.division_implementation = ml_division.implementation self.division_implementation.set_scheme( ml_division.generate_scheme()) ml_division_fct = self.division_implementation.get_function_object( ) else: ml_division_fct = Division # manage n=1 separately to avoid catastrophic propagation of errors # between log2 and exp2 to eventually compute the identity function # test-case #3 result = ConditionBlock( LogicalOr(LogicalOr(Test(vx, specifier=Test.IsNaN), Equal(n, 0)), LogicalAnd(n_is_even, vx < 0)), Return(FP_QNaN(self.precision)), Statement( ConditionBlock( Equal(n, -1, tag="n_is_mone"), #Return(Division(Constant(1, precision=self.precision), unmodified_vx, tag="div_res", precision=self.precision)), Return( ml_division_fct(Constant(1, precision=self.precision), unmodified_vx, tag="div_res", precision=self.precision)), ), ConditionBlock( # rootn( ±inf, n) is +∞ for even n< 0. Test(vx, specifier=Test.IsInfty), Statement( ConditionBlock( n < 0, #LogicalAnd(n_is_odd, n < 0), Return( Select(Test(vx, specifier=Test.IsPositiveInfty), Constant(FP_PlusZero(self.precision), precision=self.precision), Constant(FP_MinusZero(self.precision), precision=self.precision), precision=self.precision)), Return(vx), ), ), ), ConditionBlock( # rootn(±0, n) is ±∞ for odd n < 0. LogicalAnd(LogicalAnd(n_is_odd, n < 0), Equal(vx, 0), tag="n_is_odd_and_neg"), Return( Select(Test(vx, specifier=Test.IsPositiveZero), Constant(FP_PlusInfty(self.precision), precision=self.precision), Constant(FP_MinusInfty(self.precision), precision=self.precision), precision=self.precision)), ), ConditionBlock( # rootn( ±0, n) is +∞ for even n< 0. LogicalAnd(LogicalAnd(n_is_even, n < 0), Equal(vx, 0)), Return(FP_PlusInfty(self.precision))), ConditionBlock( # rootn(±0, n) is +0 for even n > 0. LogicalAnd(n_is_even, Equal(vx, 0)), Return(vx)), ConditionBlock( Equal(n, 1), Return(unmodified_vx), Return(result_sign * exp2_r * exp2_e_n_int * exp2_e_n_frac)))) return result
def piecewise_approximation(function, variable, precision, bound_low=-1.0, bound_high=1.0, num_intervals=16, max_degree=2, error_threshold=sollya.S2**-24): """ To be documented """ # table to store coefficients of the approximation on each segment coeff_table = ML_NewTable(dimensions=[num_intervals, max_degree + 1], storage_precision=precision, tag="coeff_table") error_function = lambda p, f, ai, mod, t: sollya.dirtyinfnorm(p - f, ai) max_approx_error = 0.0 interval_size = (bound_high - bound_low) / num_intervals for i in range(num_intervals): subint_low = bound_low + i * interval_size subint_high = bound_low + (i + 1) * interval_size #local_function = function(sollya.x) #local_interval = Interval(subint_low, subint_high) local_function = function(sollya.x + subint_low) local_interval = Interval(-interval_size, interval_size) local_degree = sollya.guessdegree(local_function, local_interval, error_threshold) degree = min(max_degree, local_degree) if function(subint_low) == 0.0: # if the lower bound is a zero to the function, we # need to force value=0 for the constant coefficient # and extend the approximation interval degree_list = range(1, degree + 1) poly_object, approx_error = Polynomial.build_from_approximation_with_error( function(sollya.x), degree_list, [precision] * len(degree_list), Interval(-subint_high, subint_high), sollya.absolute, error_function=error_function) else: try: poly_object, approx_error = Polynomial.build_from_approximation_with_error( local_function, degree, [precision] * (degree + 1), local_interval, sollya.absolute, error_function=error_function) except SollyaError as err: print("degree: {}".format(degree)) raise err for ci in range(degree + 1): if ci in poly_object.coeff_map: coeff_table[i][ci] = poly_object.coeff_map[ci] else: coeff_table[i][ci] = 0.0 max_approx_error = max(max_approx_error, abs(approx_error)) # computing offset diff = Subtraction(variable, Constant(bound_low, precision=precision), tag="diff", precision=precision) # delta = bound_high - bound_low delta_ratio = Constant(num_intervals / (bound_high - bound_low), precision=precision) # computing table index # index = nearestint(diff / delta * <num_intervals>) index = Max(0, Min( NearestInteger(Multiplication(diff, delta_ratio, precision=precision), precision=ML_Int32), num_intervals - 1), tag="index", debug=True, precision=ML_Int32) poly_var = Subtraction(diff, Multiplication( Conversion(index, precision=precision), Constant(interval_size, precision=precision)), precision=precision, tag="poly_var", debug=True) # generating indexed polynomial coeffs = [(ci, TableLoad(coeff_table, index, ci)) for ci in range(degree + 1)][::-1] poly_scheme = PolynomialSchemeEvaluator.generate_horner_scheme2( coeffs, poly_var, precision, {}, precision) return poly_scheme, max_approx_error