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variance neon: assert overflow conditions

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Change-Id: I12faca82d062eb33dc48dfeb39739b25112316cd
This commit is contained in:
Johann 2017-05-04 09:07:28 -07:00
parent d217c87139
commit 67ac68e399
1 changed files with 18 additions and 3 deletions
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21
vpx_dsp/arm/variance_neon.c
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@ -9,6 +9,7 @@
*/
#include <arm_neon.h>
#include <assert.h>
#include "./vpx_dsp_rtcd.h"
#include "./vpx_config.h"
@ -32,7 +33,13 @@ static INLINE int horizontal_add_s32x4(const int32x4_t v_32x4) {
return vget_lane_s32(c, 0);
}
// w * h must be less than 2048 or sum_s16 may overflow.
// The variance helper functions use int16_t for sum. 8 values are accumulated
// and then added (at which point they expand up to int32_t). To avoid overflow,
// there can be no more than 32767 / 255 ~= 128 values accumulated in each
// column. For a 32x32 buffer, this results in 32 / 8 = 4 values per row * 32
// rows = 128. Asserts have been added to each function to warn against reaching
// this limit.
// Process a block of width 4 four rows at a time.
static void variance_neon_w4x4(const uint8_t *a, int a_stride, const uint8_t *b,
int b_stride, int h, uint32_t *sse, int *sum) {
@ -41,6 +48,9 @@ static void variance_neon_w4x4(const uint8_t *a, int a_stride, const uint8_t *b,
int32x4_t sse_lo_s32 = vdupq_n_s32(0);
int32x4_t sse_hi_s32 = vdupq_n_s32(0);
// Since width is only 4, sum_s16 only loads a half row per loop.
assert(h <= 256);
for (i = 0; i < h; i += 4) {
const uint8x16_t a_u8 = load_unaligned_u8q(a, a_stride);
const uint8x16_t b_u8 = load_unaligned_u8q(b, b_stride);
@ -73,7 +83,6 @@ static void variance_neon_w4x4(const uint8_t *a, int a_stride, const uint8_t *b,
*sse = (uint32_t)horizontal_add_s32x4(vaddq_s32(sse_lo_s32, sse_hi_s32));
}
// w * h must be less than 2048 or sum_s16 may overflow.
// Process a block of any size where the width is divisible by 16.
static void variance_neon_w16(const uint8_t *a, int a_stride, const uint8_t *b,
int b_stride, int w, int h, uint32_t *sse,
@ -83,6 +92,10 @@ static void variance_neon_w16(const uint8_t *a, int a_stride, const uint8_t *b,
int32x4_t sse_lo_s32 = vdupq_n_s32(0);
int32x4_t sse_hi_s32 = vdupq_n_s32(0);
// The loop loads 16 values at a time but doubles them up when accumulating
// into sum_s16.
assert(w / 8 * h <= 128);
for (i = 0; i < h; ++i) {
for (j = 0; j < w; j += 16) {
const uint8x16_t a_u8 = vld1q_u8(a + j);
@ -117,7 +130,6 @@ static void variance_neon_w16(const uint8_t *a, int a_stride, const uint8_t *b,
*sse = (unsigned int)horizontal_add_s32x4(vaddq_s32(sse_lo_s32, sse_hi_s32));
}
// w * h must be less than 2048 or sum_s16 may overflow.
// Process a block of width 8 two rows at a time.
static void variance_neon_w8x2(const uint8_t *a, int a_stride, const uint8_t *b,
int b_stride, int h, uint32_t *sse, int *sum) {
@ -126,6 +138,9 @@ static void variance_neon_w8x2(const uint8_t *a, int a_stride, const uint8_t *b,
int32x4_t sse_lo_s32 = vdupq_n_s32(0);
int32x4_t sse_hi_s32 = vdupq_n_s32(0);
// Each column has it's own accumulator entry in sum_s16.
assert(h <= 128);
do {
const uint8x8_t a_0_u8 = vld1_u8(a);
const uint8x8_t a_1_u8 = vld1_u8(a + a_stride);