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Rewrite the Haswell SROT/DROT kernel tail loop with AVX2 to get consistent FMA rounding #5660

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Merged
martin-frbg merged 1 commit into from
Mar 4, 2026
+32 −16
Merged

Rewrite the Haswell SROT/DROT kernel tail loop with AVX2 to get consistent FMA rounding #5660

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24 changes: 16 additions & 8 deletions kernel/x86_64/drot_microk_haswell-2.c
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Original file line number Diff line number Diff line change
Expand Up @@ -12,10 +12,8 @@ static void drot_kernel(BLASLONG n, FLOAT *x, FLOAT *y, FLOAT c, FLOAT s)
BLASLONG tail_index_16 = n&(~15);

__m256d c_256, s_256;
if (n >= 4) {
c_256 = _mm256_set1_pd(c);
s_256 = _mm256_set1_pd(s);
}
c_256 = _mm256_set1_pd(c);
s_256 = _mm256_set1_pd(s);

__m256d x0, x1, x2, x3;
__m256d y0, y1, y2, y3;
Expand Down Expand Up @@ -76,10 +74,20 @@ static void drot_kernel(BLASLONG n, FLOAT *x, FLOAT *y, FLOAT c, FLOAT s)
_mm256_storeu_pd(&y[i], t0);
}

for (i = tail_index_4; i < n; ++i) {
FLOAT temp = c * x[i] + s * y[i];
y[i] = c * y[i] - s * x[i];
x[i] = temp;
if ((n & 3) > 0) {
const int64_t mask_v[8] = {-1,-1,-1,-1, 0,0,0,0};
__m256i tail_mask = _mm256_loadu_si256((__m256i*)&mask_v[4 - (n & 3)]);

x0 = _mm256_maskload_pd(&x[tail_index_4], tail_mask);
y0 = _mm256_maskload_pd(&y[tail_index_4], tail_mask);

t0 = _mm256_mul_pd(s_256, y0);
t0 = _mm256_fmadd_pd(c_256, x0, t0);
_mm256_maskstore_pd(&x[tail_index_4], tail_mask, t0);

t0 = _mm256_mul_pd(s_256, x0);
t0 = _mm256_fmsub_pd(c_256, y0, t0);
_mm256_maskstore_pd(&y[tail_index_4], tail_mask, t0);
}
}
#endif
24 changes: 16 additions & 8 deletions kernel/x86_64/srot_microk_haswell-2.c
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Original file line number Diff line number Diff line change
Expand Up @@ -13,10 +13,8 @@ static void srot_kernel(BLASLONG n, FLOAT *x, FLOAT *y, FLOAT c, FLOAT s)
BLASLONG tail_index_32 = n&(~31);

__m256 c_256, s_256;
if (n >= 8) {
c_256 = _mm256_set1_ps(c);
s_256 = _mm256_set1_ps(s);
}
c_256 = _mm256_set1_ps(c);
s_256 = _mm256_set1_ps(s);

__m256 x0, x1, x2, x3;
__m256 y0, y1, y2, y3;
Expand Down Expand Up @@ -77,10 +75,20 @@ static void srot_kernel(BLASLONG n, FLOAT *x, FLOAT *y, FLOAT c, FLOAT s)
_mm256_storeu_ps(&y[i], t0);
}

for (i = tail_index_8; i < n; ++i) {
FLOAT temp = c * x[i] + s * y[i];
y[i] = c * y[i] - s * x[i];
x[i] = temp;
if ((n & 7) > 0) {
const int32_t mask_v[16] = {-1,-1,-1,-1, -1,-1,-1,-1,0,0,0,0,0,0,0,0};
__m256i tail_mask = _mm256_loadu_si256((__m256i*)&mask_v[8 - (n & 7)]);

x0 = _mm256_maskload_ps(&x[tail_index_8], tail_mask);
y0 = _mm256_maskload_ps(&y[tail_index_8], tail_mask);

t0 = _mm256_mul_ps(s_256, y0);
t0 = _mm256_fmadd_ps(c_256, x0, t0);
_mm256_maskstore_ps(&x[tail_index_8], tail_mask, t0);

t0 = _mm256_mul_ps(s_256, x0);
t0 = _mm256_fmsub_ps(c_256, y0, t0);
_mm256_maskstore_ps(&y[tail_index_8], tail_mask, t0);
}
}
#endif
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