def length_prefix(length, offset):
"""Construct the prefix to lists or strings denoting their length.
:param length: the length of the item in bytes
:param offset: ``0x80`` when encoding raw bytes, ``0xc0`` when encoding a
list
"""
if length < 56:
return chr(offset + length)
else:
length_string = int_to_big_endian(length)
return chr(offset + 56 - 1 + len(length_string)) + length_string
def proc_modexp(ext, msg):
if not ext.post_metropolis_hardfork():
return 1, msg.gas, []
print('modexp proc', msg.gas)
baselen = msg.data.extract32(0)
explen = msg.data.extract32(32)
modlen = msg.data.extract32(64)
first_exp_bytes = msg.data.extract32(
96 + baselen) >> (8 * max(32 - explen, 0))
bitlength = -1
while first_exp_bytes:
bitlength += 1
first_exp_bytes >>= 1
adjusted_explen = max(bitlength, 0) + 8 * max(explen - 32, 0)
gas_cost = (mult_complexity(max(modlen, baselen)) *
max(adjusted_explen, 1)) // opcodes.GMODEXPQUADDIVISOR
print(baselen, explen, modlen, 'expected gas cost', gas_cost)
if msg.gas < gas_cost:
return 0, 0, []
if baselen == 0:
return 1, msg.gas - gas_cost, [0] * modlen
if modlen == 0:
return 1, msg.gas - gas_cost, []
base = bytearray(baselen)
msg.data.extract_copy(base, 0, 96, baselen)
exp = bytearray(explen)
msg.data.extract_copy(exp, 0, 96 + baselen, explen)
mod = bytearray(modlen)
msg.data.extract_copy(mod, 0, 96 + baselen + explen, modlen)
if utils.big_endian_to_int(mod) == 0:
return 1, msg.gas - gas_cost, [0] * modlen
o = pow(
utils.big_endian_to_int(base),
utils.big_endian_to_int(exp),
utils.big_endian_to_int(mod))
return 1, msg.gas - \
gas_cost, [
safe_ord(x) for x in utils.zpad(
utils.int_to_big_endian(o), modlen)]
def b64(int_bloom):
"returns b256"
return utils.zpad(utils.int_to_big_endian(int_bloom), 256)
