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Fixed and improved performance of NEON yCbCr to RGB conversion

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This commit is contained in:
Martin Fleisz 2013-02-20 05:33:42 -08:00
parent 0e19c92a20
commit b5d6b43700
1 changed files with 48 additions and 34 deletions
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82
libfreerdp/primitives/prim_colors.c
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@ -636,7 +636,12 @@ PRIM_STATIC pstatus_t neon_yCbCrToRGB_16s16s_P3P3(
int16x8_t zero = vdupq_n_s16(0);
int16x8_t max = vdupq_n_s16(255);
int16x8_t y_add = vdupq_n_s16(128);
int16x8_t r_cr = vdupq_n_s16(22986); // 1.403 << 14
int16x8_t g_cb = vdupq_n_s16(-5636); // -0.344 << 14
int16x8_t g_cr = vdupq_n_s16(-11698); // -0.714 << 14
int16x8_t b_cb = vdupq_n_s16(28999); // 1.770 << 14
int16x8_t c4096 = vdupq_n_s16(4096);
int16x8_t* y_buf = (int16x8_t*) pSrc[0];
int16x8_t* cb_buf = (int16x8_t*) pSrc[1];
@ -655,47 +660,56 @@ PRIM_STATIC pstatus_t neon_yCbCrToRGB_16s16s_P3P3(
int i;
for (i=0; i<imax; i++)
{
int16x8_t y = vld1q_s16((INT16*) (y_buf+i));
y = vaddq_s16(y, y_add);
/*
In order to use NEON signed 16-bit integer multiplication we need to convert
the floating point factors to signed int without loosing information.
The result of this multiplication is 32 bit and we have a NEON instruction
that returns the hi word of the saturated double.
Thus we will multiply the factors by the highest possible 2^n, take the
upper 16 bits of the signed 32-bit result (vqdmulhq_s16 followed by a right
shift by 1 to reverse the doubling) and correct this result by multiplying it
by 2^(16-n).
For the given factors in the conversion matrix the best possible n is 14.
int16x8_t cr = vld1q_s16((INT16*) (cr_buf+i));
Example for calculating r:
r = (y>>5) + 128 + (cr*1.403)>>5 // our base formula
r = (y>>5) + 128 + (HIWORD(cr*(1.403<<14)<<2))>>5 // see above
r = (y+4096)>>5 + (HIWORD(cr*22986)<<2)>>5 // simplification
r = ((y+4096)>>2 + HIWORD(cr*22986)) >> 3
*/
/* y = (y_buf[i] + 4096) >> 2 */
int16x8_t y = vld1q_s16((INT16*) &y_buf[i]);
y = vaddq_s16(y, c4096);
y = vshrq_n_s16(y, 2);
/* cb = cb_buf[i]; */
int16x8_t cb = vld1q_s16((INT16*)&cb_buf[i]);
/* cr = cr_buf[i]; */
int16x8_t cr = vld1q_s16((INT16*) &cr_buf[i]);
/* r = between((y + cr + (cr >> 2) + (cr >> 3) + (cr >> 5)),
* 0, 255);
*/
int16x8_t r = vaddq_s16(y, cr);
r = vaddq_s16(r, vshrq_n_s16(cr, 2));
r = vaddq_s16(r, vshrq_n_s16(cr, 3));
r = vaddq_s16(r, vshrq_n_s16(cr, 5));
/* (y + HIWORD(cr*22986)) >> 3 */
int16x8_t r = vaddq_s16(y, vshrq_n_s16(vqdmulhq_s16(cr, r_cr), 1));
r = vshrq_n_s16(r, 3);
/* r_buf[i] = MINMAX(r, 0, 255); */
r = vminq_s16(vmaxq_s16(r, zero), max);
vst1q_s16((INT16*) (r_buf+i), r);
vst1q_s16((INT16*)&r_buf[i], r);
/* cb = cb_g_buf[i]; */
int16x8_t cb = vld1q_s16((INT16*) (cb_buf+i));
/* g = between(y - (cb >> 2) - (cb >> 4) - (cb >> 5) - (cr >> 1)
* - (cr >> 3) - (cr >> 4) - (cr >> 5), 0, 255);
*/
int16x8_t g = vsubq_s16(y, vshrq_n_s16(cb, 2));
g = vsubq_s16(g, vshrq_n_s16(cb, 4));
g = vsubq_s16(g, vshrq_n_s16(cb, 5));
g = vsubq_s16(g, vshrq_n_s16(cr, 1));
g = vsubq_s16(g, vshrq_n_s16(cr, 3));
g = vsubq_s16(g, vshrq_n_s16(cr, 4));
g = vsubq_s16(g, vshrq_n_s16(cr, 5));
/* (y + HIWORD(cb*-5636) + HIWORD(cr*-11698)) >> 3 */
int16x8_t g = vaddq_s16(y, vshrq_n_s16(vqdmulhq_s16(cb, g_cb), 1));
g = vaddq_s16(g, vshrq_n_s16(vqdmulhq_s16(cr, g_cr), 1));
g = vshrq_n_s16(g, 3);
/* g_buf[i] = MINMAX(g, 0, 255); */
g = vminq_s16(vmaxq_s16(g, zero), max);
vst1q_s16((INT16*) (g_buf+i), g);
vst1q_s16((INT16*)&g_buf[i], g);
/* b = between((y + cb + (cb >> 1) + (cb >> 2) + (cb >> 6)),
* 0, 255);
*/
int16x8_t b = vaddq_s16(y, cb);
b = vaddq_s16(b, vshrq_n_s16(cb, 1));
b = vaddq_s16(b, vshrq_n_s16(cb, 2));
b = vaddq_s16(b, vshrq_n_s16(cb, 6));
/* (y + HIWORD(cb*28999)) >> 3 */
int16x8_t b = vaddq_s16(y, vshrq_n_s16(vqdmulhq_s16(cb, b_cb), 1));
b = vshrq_n_s16(b, 3);
/* b_buf[i] = MINMAX(b, 0, 255); */
b = vminq_s16(vmaxq_s16(b, zero), max);
vst1q_s16((INT16*) (b_buf+i), b);
vst1q_s16((INT16*)&b_buf[i], b);
}
y_buf += srcbump;
cb_buf += srcbump;
cr_buf += srcbump;