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quantize neon: round dqcoeff towards zero

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Add 1 if negative to get dqcoeff to round towards zero.

10-15% faster than converting to positive before shifting.

Change-Id: I01a62fd0c9bca786b6885b318bd447bb9229903d
This commit is contained in:
Johann 2017-08-21 11:23:49 -07:00
parent 13eed991f9
commit 2a5aa98a35
1 changed files with 16 additions and 27 deletions
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43
vpx_dsp/arm/quantize_neon.c
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@ -10,6 +10,7 @@
#include <arm_neon.h>
#include "./vpx_config.h"
#include "./vpx_dsp_rtcd.h"
#include "vpx_dsp/arm/mem_neon.h"
@ -154,6 +155,10 @@ void vpx_quantize_b_neon(const tran_low_t *coeff_ptr, intptr_t n_coeffs,
}
}
static INLINE int32x4_t extract_sign_bit(int32x4_t a) {
return vreinterpretq_s32_u32(vshrq_n_u32(vreinterpretq_u32_s32(a), 31));
}
// Main difference is that zbin values are halved before comparison and dqcoeff
// values are divided by 2. zbin is rounded but dqcoeff is not.
void vpx_quantize_b_32x32_neon(
@ -205,7 +210,7 @@ void vpx_quantize_b_32x32_neon(
// (round * quant * 2) >> 16 >> 1 == (round * quant) >> 16
int16x8_t qcoeff = vshrq_n_s16(vqdmulhq_s16(rounded, quant), 1);
int16x8_t dqcoeff;
int32x4_t dqcoeff_0, dqcoeff_1, dqcoeff_0_sign, dqcoeff_1_sign;
int32x4_t dqcoeff_0, dqcoeff_1;
qcoeff = vaddq_s16(qcoeff, rounded);
@ -230,21 +235,12 @@ void vpx_quantize_b_32x32_neon(
dqcoeff_0 = vmull_s16(vget_low_s16(qcoeff), vget_low_s16(dequant));
dqcoeff_1 = vmull_s16(vget_high_s16(qcoeff), vget_high_s16(dequant));
// The way the C shifts the values requires us to convert to positive before
// shifting or even narrowing, then put the sign back.
dqcoeff_0_sign = vshrq_n_s32(dqcoeff_0, 31);
dqcoeff_1_sign = vshrq_n_s32(dqcoeff_1, 31);
dqcoeff_0 = vabsq_s32(dqcoeff_0);
dqcoeff_1 = vabsq_s32(dqcoeff_1);
dqcoeff_0 = vshrq_n_s32(dqcoeff_0, 1);
dqcoeff_1 = vshrq_n_s32(dqcoeff_1, 1);
dqcoeff_0 = veorq_s32(dqcoeff_0, dqcoeff_0_sign);
dqcoeff_1 = veorq_s32(dqcoeff_1, dqcoeff_1_sign);
dqcoeff_0 = vsubq_s32(dqcoeff_0, dqcoeff_0_sign);
dqcoeff_1 = vsubq_s32(dqcoeff_1, dqcoeff_1_sign);
// Add 1 if negative to round towards zero because the C uses division.
dqcoeff_0 = vaddq_s32(dqcoeff_0, extract_sign_bit(dqcoeff_0));
dqcoeff_1 = vaddq_s32(dqcoeff_1, extract_sign_bit(dqcoeff_1));
// Narrow *without saturation* because that's what the C does.
dqcoeff = vcombine_s16(vmovn_s32(dqcoeff_0), vmovn_s32(dqcoeff_1));
dqcoeff =
vcombine_s16(vshrn_n_s32(dqcoeff_0, 1), vshrn_n_s32(dqcoeff_1, 1));
store_s16q_to_tran_low(dqcoeff_ptr, dqcoeff);
dqcoeff_ptr += 8;
@ -274,7 +270,7 @@ void vpx_quantize_b_32x32_neon(
// (round * quant * 2) >> 16 >> 1 == (round * quant) >> 16
int16x8_t qcoeff = vshrq_n_s16(vqdmulhq_s16(rounded, quant), 1);
int16x8_t dqcoeff;
int32x4_t dqcoeff_0, dqcoeff_1, dqcoeff_0_sign, dqcoeff_1_sign;
int32x4_t dqcoeff_0, dqcoeff_1;
qcoeff = vaddq_s16(qcoeff, rounded);
@ -300,18 +296,11 @@ void vpx_quantize_b_32x32_neon(
dqcoeff_0 = vmull_s16(vget_low_s16(qcoeff), vget_low_s16(dequant));
dqcoeff_1 = vmull_s16(vget_high_s16(qcoeff), vget_high_s16(dequant));
dqcoeff_0_sign = vshrq_n_s32(dqcoeff_0, 31);
dqcoeff_1_sign = vshrq_n_s32(dqcoeff_1, 31);
dqcoeff_0 = vabsq_s32(dqcoeff_0);
dqcoeff_1 = vabsq_s32(dqcoeff_1);
dqcoeff_0 = vshrq_n_s32(dqcoeff_0, 1);
dqcoeff_1 = vshrq_n_s32(dqcoeff_1, 1);
dqcoeff_0 = veorq_s32(dqcoeff_0, dqcoeff_0_sign);
dqcoeff_1 = veorq_s32(dqcoeff_1, dqcoeff_1_sign);
dqcoeff_0 = vsubq_s32(dqcoeff_0, dqcoeff_0_sign);
dqcoeff_1 = vsubq_s32(dqcoeff_1, dqcoeff_1_sign);
dqcoeff_0 = vaddq_s32(dqcoeff_0, extract_sign_bit(dqcoeff_0));
dqcoeff_1 = vaddq_s32(dqcoeff_1, extract_sign_bit(dqcoeff_1));
dqcoeff = vcombine_s16(vmovn_s32(dqcoeff_0), vmovn_s32(dqcoeff_1));
dqcoeff =
vcombine_s16(vshrn_n_s32(dqcoeff_0, 1), vshrn_n_s32(dqcoeff_1, 1));
store_s16q_to_tran_low(dqcoeff_ptr, dqcoeff);
dqcoeff_ptr += 8;