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ppc: reduce overreads when loading 8 pixels in altivec dsp functions

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Altivec can only load naturally aligned vectors. To handle possibly
unaligned data a second vector is loaded from an offset of the original
location and the data is recovered through a vector permutation.
Overreads are minimal if the offset for second load points to the last
element of data. This is 7 for loading eight 8-bit pixels and overreads
are reduced from 16 bytes to 8 bytes if the pixels are 64-bit aligned.
For unaligned pixels the overread is reduced from 23 bytes to 15 bytes
in the worst case.
This commit is contained in:
Janne Grunau 2014-02-13 12:27:17 +01:00
parent 3fbad00714
commit 98fdfa9970
1 changed files with 10 additions and 10 deletions
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20
libavcodec/ppc/dsputil_altivec.c
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@ -285,10 +285,10 @@ static int sad8_altivec(void *v, uint8_t *pix1, uint8_t *pix2, int line_size, in
/* Read potentially unaligned pixels into t1 and t2
Since we're reading 16 pixels, and actually only want 8,
mask out the last 8 pixels. The 0s don't change the sum. */
vector unsigned char pix1l = vec_ld( 0, pix1);
vector unsigned char pix1r = vec_ld(15, pix1);
vector unsigned char pix2l = vec_ld( 0, pix2);
vector unsigned char pix2r = vec_ld(15, pix2);
vector unsigned char pix1l = vec_ld(0, pix1);
vector unsigned char pix1r = vec_ld(7, pix1);
vector unsigned char pix2l = vec_ld(0, pix2);
vector unsigned char pix2r = vec_ld(7, pix2);
t1 = vec_and(vec_perm(pix1l, pix1r, perm1), permclear);
t2 = vec_and(vec_perm(pix2l, pix2r, perm2), permclear);
@ -367,10 +367,10 @@ static int sse8_altivec(void *v, uint8_t *pix1, uint8_t *pix2, int line_size, in
/* Read potentially unaligned pixels into t1 and t2
Since we're reading 16 pixels, and actually only want 8,
mask out the last 8 pixels. The 0s don't change the sum. */
vector unsigned char pix1l = vec_ld( 0, pix1);
vector unsigned char pix1r = vec_ld(15, pix1);
vector unsigned char pix2l = vec_ld( 0, pix2);
vector unsigned char pix2r = vec_ld(15, pix2);
vector unsigned char pix1l = vec_ld(0, pix1);
vector unsigned char pix1r = vec_ld(7, pix1);
vector unsigned char pix2l = vec_ld(0, pix2);
vector unsigned char pix2r = vec_ld(7, pix2);
t1 = vec_and(vec_perm(pix1l, pix1r, perm1), permclear);
t2 = vec_and(vec_perm(pix2l, pix2r, perm2), permclear);
@ -489,8 +489,8 @@ static void get_pixels_altivec(int16_t *restrict block, const uint8_t *pixels, i
// Read potentially unaligned pixels.
// We're reading 16 pixels, and actually only want 8,
// but we simply ignore the extras.
vector unsigned char pixl = vec_ld( 0, pixels);
vector unsigned char pixr = vec_ld(15, pixels);
vector unsigned char pixl = vec_ld(0, pixels);
vector unsigned char pixr = vec_ld(7, pixels);
bytes = vec_perm(pixl, pixr, perm);
// convert the bytes into shorts