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NEON: speed-up strong filtering

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The sub-expression trick removes two constants and
two vmlal_s8 instructions.

Change-Id: I200022573b4880871b528b13a11a8f3d95def113
This commit is contained in:
Pascal Massimino 2017-01-19 09:33:47 -08:00
parent 73f567ea8b
commit 71c53f1aeb
1 changed files with 17 additions and 16 deletions
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33
src/dsp/dec_neon.c
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@ -755,24 +755,25 @@ static void ApplyFilter6(
const int8x16_t delta,
uint8x16_t* const op2, uint8x16_t* const op1, uint8x16_t* const op0,
uint8x16_t* const oq0, uint8x16_t* const oq1, uint8x16_t* const oq2) {
const int16x8_t kCst63 = vdupq_n_s16(63);
const int8x8_t kCst27 = vdup_n_s8(27);
const int8x8_t kCst18 = vdup_n_s8(18);
const int8x8_t kCst9 = vdup_n_s8(9);
// We have to compute: X = (9*a+63) >> 7, Y = (18*a+63)>>7, Z = (27*a+63) >> 7
// Turns out, there's a common sub-expression S=9 * a - 1 that can be used
// with the special vqrshrn_n_s16 rounding-shift-and-narrow instruction:
// X = (S + 64) >> 7, Y = (S + 32) >> 6, Z = (18 * a + S + 64) >> 7
const int8x8_t delta_lo = vget_low_s8(delta);
const int8x8_t delta_hi = vget_high_s8(delta);
const int16x8_t s1_lo = vmlal_s8(kCst63, kCst27, delta_lo); // 63 + 27 * a
const int16x8_t s1_hi = vmlal_s8(kCst63, kCst27, delta_hi); // 63 + 27 * a
const int16x8_t s2_lo = vmlal_s8(kCst63, kCst18, delta_lo); // 63 + 18 * a
const int16x8_t s2_hi = vmlal_s8(kCst63, kCst18, delta_hi); // 63 + 18 * a
const int16x8_t s3_lo = vmlal_s8(kCst63, kCst9, delta_lo); // 63 + 9 * a
const int16x8_t s3_hi = vmlal_s8(kCst63, kCst9, delta_hi); // 63 + 9 * a
const int8x8_t a1_lo = vqshrn_n_s16(s1_lo, 7);
const int8x8_t a1_hi = vqshrn_n_s16(s1_hi, 7);
const int8x8_t a2_lo = vqshrn_n_s16(s2_lo, 7);
const int8x8_t a2_hi = vqshrn_n_s16(s2_hi, 7);
const int8x8_t a3_lo = vqshrn_n_s16(s3_lo, 7);
const int8x8_t a3_hi = vqshrn_n_s16(s3_hi, 7);
const int8x8_t kCst9 = vdup_n_s8(9);
const int16x8_t kCstm1 = vdupq_n_s16(-1);
const int8x8_t kCst18 = vdup_n_s8(18);
const int16x8_t S_lo = vmlal_s8(kCstm1, kCst9, delta_lo); // S = 9 * a - 1
const int16x8_t S_hi = vmlal_s8(kCstm1, kCst9, delta_hi);
const int16x8_t Z_lo = vmlal_s8(S_lo, kCst18, delta_lo); // S + 18 * a
const int16x8_t Z_hi = vmlal_s8(S_hi, kCst18, delta_hi);
const int8x8_t a3_lo = vqrshrn_n_s16(S_lo, 7); // (9 * a + 63) >> 7
const int8x8_t a3_hi = vqrshrn_n_s16(S_hi, 7);
const int8x8_t a2_lo = vqrshrn_n_s16(S_lo, 6); // (9 * a + 31) >> 6
const int8x8_t a2_hi = vqrshrn_n_s16(S_hi, 6);
const int8x8_t a1_lo = vqrshrn_n_s16(Z_lo, 7); // (27 * a + 63) >> 7
const int8x8_t a1_hi = vqrshrn_n_s16(Z_hi, 7);
const int8x16_t a1 = vcombine_s8(a1_lo, a1_hi);
const int8x16_t a2 = vcombine_s8(a2_lo, a2_hi);
const int8x16_t a3 = vcombine_s8(a3_lo, a3_hi);