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| author | Johann <johannkoenig@google.com> | 2016-08-02 15:59:35 -0700 |
|---|---|---|
| committer | Johann <johannkoenig@google.com> | 2016-09-23 17:04:18 -0700 |
| commit | ab0e7a237a6e9796c15a8858caac04dea3593d62 (patch) | |
| tree | 359cb7482dca32b87306efb67101c48c616dfcb8 /vp8/common/arm/neon | |
| parent | ada850786c7e0a5d6024b7716db9896124fd483e (diff) | |
| download | libvpx-ab0e7a237a6e9796c15a8858caac04dea3593d62.tar libvpx-ab0e7a237a6e9796c15a8858caac04dea3593d62.tar.gz libvpx-ab0e7a237a6e9796c15a8858caac04dea3593d62.tar.bz2 libvpx-ab0e7a237a6e9796c15a8858caac04dea3593d62.zip | |
Use shifted value for sinpi8sqrt2
The value 35468 changes sign when stored in int16_t:
implicit conversion from 'int' to 'int16_t' (aka 'short')
changes value from 35468 to -30068
This negation requires adding back the original value to compensate.
Shifting the value keeps the value positive and saves a post-vqdmulh
shift.
This technique is used in webp and idct_dequant_full_2x_neon
BUG=b/28027557
Change-Id: I0c5ce09bea170fe08061856c2af6f841a557e0c3
Diffstat (limited to 'vp8/common/arm/neon')
| -rw-r--r-- | vp8/common/arm/neon/dequant_idct_neon.c | 10 | ||||
| -rw-r--r-- | vp8/common/arm/neon/shortidct4x4llm_neon.c | 10 |
2 files changed, 10 insertions, 10 deletions
diff --git a/vp8/common/arm/neon/dequant_idct_neon.c b/vp8/common/arm/neon/dequant_idct_neon.c index ff5981eaa..753051c77 100644 --- a/vp8/common/arm/neon/dequant_idct_neon.c +++ b/vp8/common/arm/neon/dequant_idct_neon.c @@ -11,7 +11,11 @@ #include <arm_neon.h> static const int16_t cospi8sqrt2minus1 = 20091; -static const int16_t sinpi8sqrt2 = 35468; +// 35468 exceeds INT16_MAX and gets converted to a negative number. Because of +// the way it is used in vqdmulh, where the result is doubled, it can be divided +// by 2 beforehand. This saves compensating for the negative value as well as +// shifting the result. +static const int16_t sinpi8sqrt2 = 35468 >> 1; void vp8_dequant_idct_add_neon(int16_t *input, int16_t *dq, unsigned char *dst, int stride) { @@ -60,10 +64,8 @@ void vp8_dequant_idct_add_neon(int16_t *input, int16_t *dq, unsigned char *dst, q3 = vqdmulhq_n_s16(q2, sinpi8sqrt2); q4 = vqdmulhq_n_s16(q2, cospi8sqrt2minus1); - q3 = vshrq_n_s16(q3, 1); q4 = vshrq_n_s16(q4, 1); - q3 = vqaddq_s16(q3, q2); q4 = vqaddq_s16(q4, q2); d10 = vqsub_s16(vget_low_s16(q3), vget_high_s16(q4)); @@ -90,10 +92,8 @@ void vp8_dequant_idct_add_neon(int16_t *input, int16_t *dq, unsigned char *dst, d12 = vqadd_s16(d2tmp2.val[0], d2tmp3.val[0]); d13 = vqsub_s16(d2tmp2.val[0], d2tmp3.val[0]); - q3 = vshrq_n_s16(q3, 1); q4 = vshrq_n_s16(q4, 1); - q3 = vqaddq_s16(q3, q2); q4 = vqaddq_s16(q4, q2); d10 = vqsub_s16(vget_low_s16(q3), vget_high_s16(q4)); diff --git a/vp8/common/arm/neon/shortidct4x4llm_neon.c b/vp8/common/arm/neon/shortidct4x4llm_neon.c index a36c0c1ca..1adb1c317 100644 --- a/vp8/common/arm/neon/shortidct4x4llm_neon.c +++ b/vp8/common/arm/neon/shortidct4x4llm_neon.c @@ -11,7 +11,11 @@ #include <arm_neon.h> static const int16_t cospi8sqrt2minus1 = 20091; -static const int16_t sinpi8sqrt2 = 35468; +// 35468 exceeds INT16_MAX and gets converted to a negative number. Because of +// the way it is used in vqdmulh, where the result is doubled, it can be divided +// by 2 beforehand. This saves compensating for the negative value as well as +// shifting the result. +static const int16_t sinpi8sqrt2 = 35468 >> 1; void vp8_short_idct4x4llm_neon(int16_t *input, unsigned char *pred_ptr, int pred_stride, unsigned char *dst_ptr, @@ -40,10 +44,8 @@ void vp8_short_idct4x4llm_neon(int16_t *input, unsigned char *pred_ptr, d12 = vqadd_s16(vget_low_s16(q1s16), vget_high_s16(q1s16)); // a1 d13 = vqsub_s16(vget_low_s16(q1s16), vget_high_s16(q1s16)); // b1 - q3s16 = vshrq_n_s16(q3s16, 1); q4s16 = vshrq_n_s16(q4s16, 1); - q3s16 = vqaddq_s16(q3s16, q2s16); q4s16 = vqaddq_s16(q4s16, q2s16); d10 = vqsub_s16(vget_low_s16(q3s16), vget_high_s16(q4s16)); // c1 @@ -71,10 +73,8 @@ void vp8_short_idct4x4llm_neon(int16_t *input, unsigned char *pred_ptr, d12 = vqadd_s16(vget_low_s16(q1s16), vget_high_s16(q1s16)); // a1 d13 = vqsub_s16(vget_low_s16(q1s16), vget_high_s16(q1s16)); // b1 - q3s16 = vshrq_n_s16(q3s16, 1); q4s16 = vshrq_n_s16(q4s16, 1); - q3s16 = vqaddq_s16(q3s16, q2s16); q4s16 = vqaddq_s16(q4s16, q2s16); d10 = vqsub_s16(vget_low_s16(q3s16), vget_high_s16(q4s16)); // c1 |