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rtl_sdr_fm: vectorize rotate+widen path: add AVX2/NEON implementations for widen_rotate90_u8_to_s16_bias127 with scalar tail fallback. This applies the 90° rotation and bias-127 widening in vectors to reduce callback CPU without changing behavior.

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arancormonk
2025-09-03 22:23:05 -04:00
parent 1b9c3aa659
commit 391048a45a
1 changed files with 59 additions and 6 deletions
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65
src/rtl_sdr_fm.cpp
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@@ -158,34 +158,87 @@ static inline void widen_u8_to_s16_bias127(const unsigned char * DSD_FME_RESTRIC
static inline void widen_rotate90_u8_to_s16_bias127(const unsigned char * DSD_FME_RESTRICT src,
int16_t * DSD_FME_RESTRICT dst, uint32_t len)
{
/* len is expected to be even (I/Q interleaved). Process in 8-byte blocks (4 IQ pairs). */
#if defined(__AVX2__)
/* AVX2 path: process 32 bytes per loop, applying rotation+wide.
Pattern per 8-byte group: [0,1,3,2,4,5,7,6] with select mask for 128-x on lanes {2,4,5,7}. */
const __m256i shuffle = _mm256_setr_epi8(
0, 1, 3, 2, 4, 5, 7, 6, 8, 9,11,10,12,13,15,14,
0, 1, 3, 2, 4, 5, 7, 6, 8, 9,11,10,12,13,15,14);
const __m256i mask_sel = _mm256_setr_epi16(
0x0000,0x0000,0xFFFF,0x0000,0xFFFF,0xFFFF,0x0000,0xFFFF,
0x0000,0x0000,0xFFFF,0x0000,0xFFFF,0xFFFF,0x0000,0xFFFF);
const __m256i c127 = _mm256_set1_epi16(127);
const __m256i c128 = _mm256_set1_epi16(128);
uint32_t i = 0;
for (; i + 32 <= len; i += 32) {
__m256i v8 = _mm256_loadu_si256((const __m256i*)(src + i));
__m256i sh = _mm256_shuffle_epi8(v8, shuffle);
__m128i sh_lo = _mm256_castsi256_si128(sh);
__m128i sh_hi = _mm256_extracti128_si256(sh, 1);
__m256i v16_lo = _mm256_cvtepu8_epi16(sh_lo);
__m256i v16_hi = _mm256_cvtepu8_epi16(sh_hi);
__m256i bs_lo = _mm256_sub_epi16(v16_lo, c127);
__m256i bm_lo = _mm256_sub_epi16(c128, v16_lo);
__m256i bs_hi = _mm256_sub_epi16(v16_hi, c127);
__m256i bm_hi = _mm256_sub_epi16(c128, v16_hi);
__m256i out_lo = _mm256_blendv_epi8(bs_lo, bm_lo, mask_sel);
__m256i out_hi = _mm256_blendv_epi8(bs_hi, bm_hi, mask_sel);
_mm256_storeu_si256((__m256i*)(dst + i), out_lo);
_mm256_storeu_si256((__m256i*)(dst + i + 16), out_hi);
}
#elif defined(__ARM_NEON) || defined(__ARM_NEON__)
/* NEON path: process 16 bytes per loop */
const uint8x16_t tbl_idx = {0,1,3,2,4,5,7,6, 8,9,11,10,12,13,15,14};
const int16x8_t c127 = vdupq_n_s16(127);
const int16x8_t c128 = vdupq_n_s16(128);
/* mask lanes to select 128-x for lanes {2,4,5,7} in each 8-lane group */
const uint16_t mpat[8] = {0x0000,0x0000,0xFFFF,0x0000,0xFFFF,0xFFFF,0x0000,0xFFFF};
const uint16x8_t msel = vld1q_u16(mpat);
uint32_t i = 0;
for (; i + 16 <= len; i += 16) {
uint8x16_t v = vld1q_u8(src + i);
/* lane-wise shuffle */
uint8x16_t sh = vqtbl1q_u8(v, tbl_idx);
/* widen low */
uint8x8_t sh_lo8 = vget_low_u8(sh);
uint8x8_t sh_hi8 = vget_high_u8(sh);
int16x8_t v16_lo = vreinterpretq_s16_u16(vmovl_u8(sh_lo8));
int16x8_t v16_hi = vreinterpretq_s16_u16(vmovl_u8(sh_hi8));
int16x8_t bs_lo = vsubq_s16(v16_lo, c127);
int16x8_t bm_lo = vsubq_s16(c128, v16_lo);
int16x8_t bs_hi = vsubq_s16(v16_hi, c127);
int16x8_t bm_hi = vsubq_s16(c128, v16_hi);
/* blend: out = (msel ? bm : bs), msel repeated for both halves */
int16x8_t out_lo = vbslq_s16(msel, bm_lo, bs_lo);
int16x8_t out_hi = vbslq_s16(msel, bm_hi, bs_hi);
vst1q_s16(dst + i, out_lo);
vst1q_s16(dst + i + 8, out_hi);
}
#else
uint32_t i = 0;
#endif
/* Scalar tail or generic path */
for (; i + 8 <= len; i += 8) {
/* sample 0: multiply by 1 */
int16_t i0 = (int16_t)src[i + 0] - 127;
int16_t q0 = (int16_t)src[i + 1] - 127;
dst[i + 0] = i0;
dst[i + 1] = q0;
/* sample 1: multiply by j -> (1 - Q, I) to match unsigned 255-x behavior */
int16_t i1 = (int16_t)src[i + 2] - 127;
int16_t q1 = (int16_t)src[i + 3] - 127;
dst[i + 2] = (int16_t)(1 - q1);
dst[i + 3] = i1;
/* sample 2: multiply by -1 -> (1 - I, 1 - Q) */
int16_t i2 = (int16_t)src[i + 4] - 127;
int16_t q2 = (int16_t)src[i + 5] - 127;
dst[i + 4] = (int16_t)(1 - i2);
dst[i + 5] = (int16_t)(1 - q2);
/* sample 3: multiply by -j -> (Q, 1 - I) */
int16_t i3 = (int16_t)src[i + 6] - 127;
int16_t q3 = (int16_t)src[i + 7] - 127;
dst[i + 6] = q3;
dst[i + 7] = (int16_t)(1 - i3);
}
/* Tail (up to 3 IQ pairs). Match original semantics: no rotation applied, widen only. */
for (; i + 1 < len; i += 2) {
dst[i + 0] = (int16_t)src[i + 0] - 127;
dst[i + 1] = (int16_t)src[i + 1] - 127;