pure_to_radix.cpp

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#include "barretenberg/vm2/simulation/standalone/pure_to_radix.hpp"
 
#include <algorithm>
#include <cstdint>
 
#include "barretenberg/common/bb_bench.hpp"
#include "barretenberg/numeric/uint256/uint256.hpp"
#include "barretenberg/vm2/common/aztec_constants.hpp"
#include "barretenberg/vm2/simulation/interfaces/memory.hpp"
 
namespace bb::avm2::simulation {
 
std::pair<std::vector<uint8_t>, /* truncated */ bool> PureToRadix::to_le_radix(const FF& value,
                                                                               uint32_t num_limbs,
                                                                               uint32_t radix)
{
    BB_BENCH_NAME("PureToRadix::to_le_radix");
 
    uint256_t value_integer = static_cast<uint256_t>(value);
    std::vector<uint8_t> limbs;
    limbs.reserve(num_limbs);
 
    for (uint32_t i = 0; i < num_limbs; i++) {
        auto [quotient, remainder] = value_integer.divmod(static_cast<uint64_t>(radix));
        limbs.push_back(static_cast<uint8_t>(remainder));
        value_integer = quotient;
    }
 
    return { limbs, value_integer != 0 };
}
 
std::pair<std::vector<bool>, /* truncated */ bool> PureToRadix::to_le_bits(const FF& value, uint32_t num_limbs)
{
    BB_BENCH_NAME("PureToRadix::to_le_bits");
 
    const auto [limbs, truncated] = to_le_radix(value, num_limbs, 2);
    std::vector<bool> bits(limbs.size());
 
    std::transform(limbs.begin(), limbs.end(), bits.begin(), [](uint8_t val) {
        return val != 0; // Convert nonzero values to `true`, zero to `false`
    });
 
    return { bits, truncated };
}
 
void PureToRadix::to_be_radix(MemoryInterface& memory,
                              const FF& value,
                              uint32_t radix,
                              uint32_t num_limbs,
                              bool is_output_bits,
                              MemoryAddress dst_addr)
{
    BB_BENCH_NAME("PureToRadix::to_be_radix");
 
    uint64_t write_addr_upper_bound = static_cast<uint64_t>(dst_addr) + num_limbs;
    bool dst_out_of_range = write_addr_upper_bound > AVM_MEMORY_SIZE;
    // Error handling - check that the radix value is within the valid range
    // The valid range is [2, 256]. Therefore, the radix is invalid if (2 > radix) or (radix > 256)
    // We need to perform both checks explicitly since that is what the circuit would do
    bool radix_is_lt_2 = radix < 2;
    bool radix_is_gt_256 = radix > 256;
    // Error handling - check that if is_output_bits is true, the radix has to be 2
    bool invalid_bitwise_radix = is_output_bits && (radix != 2);
    // Error handling - if num_limbs is zero, value needs to be zero
    bool invalid_num_limbs = (num_limbs == 0) && !value.is_zero();
 
    if (dst_out_of_range || radix_is_lt_2 || radix_is_gt_256 || invalid_bitwise_radix || invalid_num_limbs) {
        throw ToRadixException("Invalid parameters for ToRadix");
    }
 
    if (is_output_bits) {
        auto [limbs, truncated] = to_le_bits(value, num_limbs);
        if (truncated) {
            throw ToRadixException("Truncation error");
        }
        std::reverse(limbs.begin(), limbs.end());
        for (uint32_t i = 0; i < num_limbs; i++) {
            memory.set(dst_addr + i, MemoryValue::from<uint1_t>(static_cast<uint1_t>(limbs[i])));
        }
    } else {
        auto [limbs, truncated] = to_le_radix(value, num_limbs, radix);
        if (truncated) {
            throw ToRadixException("Truncation error");
        }
        std::ranges::reverse(limbs);
        for (uint32_t i = 0; i < num_limbs; i++) {
            memory.set(dst_addr + i, MemoryValue::from<uint8_t>(limbs[i]));
        }
    }
}
 
} // namespace bb::avm2::simulation