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compute constant terms for same row only once

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Ahmet Inan 2023-06-05 08:33:29 +02:00
commit 6ec9fcba1a
1 changed files with 24 additions and 0 deletions
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24
cauchy_reed_solomon_erasure_coding.hh
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@ -25,6 +25,7 @@ struct CauchyReedSolomonErasureCoding
typedef typename GF::value_type value_type;
typedef typename GF::ValueType ValueType;
typedef typename GF::IndexType IndexType;
IndexType row_num, row_den;
// $a_{ij} = \frac{1}{x_i + y_j}$
IndexType cauchy_matrix(int i, int j)
{
@ -34,6 +35,7 @@ struct CauchyReedSolomonErasureCoding
// $b_{ij} = \frac{\prod_{k=1}^{n}{(x_j + y_k)(x_k + y_i)}}{(x_j + y_i)\prod_{k \ne j}^{n}{(x_j - x_k)}\prod_{k \ne i}^{n}{(y_i - y_k)}}$
IndexType inverse_cauchy_matrix(const ValueType *rows, int i, int j, int n)
{
#if 0
ValueType col_i(ValueType::N - i);
IndexType prod_xy(0), prod_x(0), prod_y(0);
for (int k = 0; k < n; k++) {
@ -45,6 +47,28 @@ struct CauchyReedSolomonErasureCoding
prod_y *= index(col_i + col_k);
}
return prod_xy / (index(rows[j] + col_i) * prod_x * prod_y);
#else
ValueType col_i(ValueType::N - i);
if (j == 0) {
IndexType num(0), den(0);
for (int k = 0; k < n; k++) {
ValueType col_k(ValueType::N - k);
num *= index(rows[k] + col_i);
if (k != i)
den *= index(col_i + col_k);
}
row_num = num;
row_den = den;
}
IndexType num(row_num), den(row_den);
for (int k = 0; k < n; k++) {
ValueType col_k(ValueType::N - k);
num *= index(rows[j] + col_k);
if (k != j)
den *= index(rows[j] + rows[k]);
}
return num / (index(rows[j] + col_i) * den);
#endif
}
#if defined(__ARM_NEON) && !defined(__aarch64__)
static inline uint8x16_t vqtbl1q_u8(uint8x16_t lut, uint8x16_t idx)