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fix modexp type mismatch #414

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fix modexp type mismatch #414

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26 changes: 21 additions & 5 deletions src/halmos/sevm.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2165,14 +2165,30 @@ def call_unknown() -> None:
# modexp
elif eq(to, con_addr(5)):
exit_code = con(1)
modulus_size = ex.int_of(extract_bytes(arg, 64, 32))

# lengths in bytes
base_len = ex.int_of(arg.get_word(0))
exponent_len = ex.int_of(arg.get_word(32))
modulus_len = ex.int_of(arg.get_word(64))
input_len = base_len + exponent_len + modulus_len

# The rest of the input is discarded.
# Whenever the input is too short,
# the missing bytes are considered to be zero.
modexp_input = arg.slice(96, 96 + input_len)

# lengths in bits
input_bitsize = input_len * 8
modulus_bitsize = modulus_len * 8

f_modexp = Function(
f"f_modexp_{arg_size}_{modulus_size}",
BitVecSorts[arg_size],
BitVecSorts[modulus_size],
f"f_modexp_{input_bitsize}_{modulus_bitsize}",
BitVecSorts[input_bitsize],
BitVecSorts[modulus_bitsize],
)

# TODO: empty returndata in error
ret = ByteVec(f_modexp(arg))
ret = ByteVec(f_modexp(modexp_input.unwrap()))

# ecadd
elif eq(to, con_addr(6)):
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