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fix(balanced_decomposition): reconstruct modulus from limbs #1028

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fix(balanced_decomposition): reconstruct modulus from limbs #1028

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1f41860
fix(balanced_decomposition): reconstruct modulus from limbs
VolodymyrBg Aug 13, 2025
af49ee4
Update balanced_decomposition.h
VolodymyrBg Aug 13, 2025
d5b4ba6
Update cpu_balanced_decomposition.cpp
VolodymyrBg Aug 13, 2025
bc41a46
fix formatting
VolodymyrBg Sep 10, 2025
5da4caa
fix formatting
VolodymyrBg Sep 10, 2025
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10 changes: 6 additions & 4 deletions icicle/include/icicle/balanced_decomposition.h
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
#pragma once

#include "icicle/vec_ops.h" // For VecOpsConfig
#include <cmath>

namespace icicle {
namespace balanced_decomposition {
Expand Down Expand Up @@ -36,10 +37,11 @@ namespace icicle {
static_assert(T::TLC == 2, "Balanced decomposition assumes q ~64-bit");

constexpr auto q_storage = T::get_modulus();
const int64_t q = *(const int64_t*)&q_storage;
ICICLE_ASSERT(q > 0) << "Expecting at least one slack bit to use int64 arithmetic";
const uint64_t q_u = (static_cast<uint64_t>(q_storage.limbs[0])) |

@yshekel yshekel Aug 13, 2025

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(1) I think you assume limbs are 32b so please add a static assert
(2) now that it is uint64, the ICICLE_ASSERT(q_u > 0) is redundant since uint is always >0. The original intent was to make sure we have a slack bit.
(3) If I recall correctly similar code also exists in cpu_balanced_decomposition code, please fix it as well.

(static_cast<uint64_t>(q_storage.limbs[1]) << 32);
ICICLE_ASSERT(q_u > 0) << "Expecting at least one slack bit to use 64-bit arithmetic";

const double log2_q = std::log2(static_cast<double>(q));
const double log2_q = std::log2(static_cast<double>(q_u));
const double log2_b = std::log2(static_cast<double>(base));
const uint32_t digits = static_cast<uint32_t>(std::ceil(log2_q / log2_b));

Expand Down Expand Up @@ -108,4 +110,4 @@ namespace icicle {
const T* input, size_t input_size, uint32_t base, const VecOpsConfig& config, T* output, size_t output_size);

} // namespace balanced_decomposition
} // namespace icicle
} // namespace icicle
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