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fix: Fuzzer sometimes creates to radix with num_limbs=0 #19929

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Merged
sirasistant merged 1 commit into from
Jan 26, 2026
Merged

fix: Fuzzer sometimes creates to radix with num_limbs=0 #19929

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10 changes: 7 additions & 3 deletions barretenberg/cpp/src/barretenberg/avm_fuzzer/mutations/instructions/instruction.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -695,7 +695,7 @@ std::vector<FuzzInstruction> InstructionMutator::generate_toradixbe_instruction(
.value = static_cast<uint8_t>(is_output_bits ? 1 : 0) });

// Generate value with num_limbs digits
uint32_t num_limbs = std::uniform_int_distribution<uint32_t>(1, 256)(rng);
uint32_t num_limbs = std::uniform_int_distribution<uint32_t>(0, 256)(rng);
bb::avm2::FF value = 0;
bb::avm2::FF exponent = 1;
for (uint32_t i = 0; i < num_limbs; i++) {
Expand All @@ -704,9 +704,13 @@ std::vector<FuzzInstruction> InstructionMutator::generate_toradixbe_instruction(
exponent *= radix;
}

// 20% chance to truncate - reduce the number of limbs we request
// 20% chance to truncate - reduce the number of limbs we request or increment the value if we have 0 limbs
if (std::uniform_int_distribution<int>(0, 4)(rng) == 0) {
num_limbs--;
if (num_limbs > 0) {
num_limbs--;
} else {
value++;
}
}

// SET the num_limbs (U32)
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