[pulseaudio-discuss] [PATCH v3] sconv: Change/fix conversion to/from float32

Peter Meerwald pmeerw at pmeerw.net
Sun Feb 3 16:30:19 PST 2013


From: Peter Meerwald <p.meerwald at bct-electronic.com>

use (1<<15) instead of 0x7fff as a factor when converting from s16 to float32
use (1<<31) instead of 0x7fffffff as a factor when converting from s32 to float32

the change is motivated by the following desireable properties:
* s16_from_f32(f32_from_s16(x)) == x for all possible s16 values
* x / (1.0f << 15) == x * (1.0f / (1 << 15)) for all x in s16

above changes enable easier optimization while guaranteeing bit-exact results

further, other audio sample conversion code (libavresample) does it the same way

v3 (comments Tanu):
* fix saturation in pa_sconv_s16le_from_f32ne_neon(), use vqrshrn
v2 (comments Tanu):
* fix comments in ARM NEON code
* use llrintf() in pa_sconv_s32le_from_float32ne()

Signed-off-by: Peter Meerwald <p.meerwald at bct-electronic.com>
Cc: Tanu Kaskinen <tanuk at iki.fi>
---
 src/pulsecore/sconv-s16le.c | 84 ++++++++++++++++++++-------------------------
 src/pulsecore/sconv_neon.c  | 25 ++++++--------
 src/pulsecore/sconv_sse.c   | 66 +++++++++++++++++------------------
 3 files changed, 79 insertions(+), 96 deletions(-)

diff --git a/src/pulsecore/sconv-s16le.c b/src/pulsecore/sconv-s16le.c
index 138e418..45cf972 100644
--- a/src/pulsecore/sconv-s16le.c
+++ b/src/pulsecore/sconv-s16le.c
@@ -85,11 +85,11 @@ void pa_sconv_s16le_to_float32ne(unsigned n, const int16_t *a, float *b) {
 #if SWAP_WORDS == 1
     for (; n > 0; n--) {
         int16_t s = *(a++);
-        *(b++) = ((float) INT16_FROM(s))/(float) 0x7FFF;
+        *(b++) = INT16_FROM(s) * (1.0f / (1 << 15));
     }
 #else
     for (; n > 0; n--)
-        *(b++) = ((float) (*(a++)))/(float) 0x7FFF;
+        *(b++) = *(a++) * (1.0f / (1 << 15));
 #endif
 }
 
@@ -100,11 +100,11 @@ void pa_sconv_s32le_to_float32ne(unsigned n, const int32_t *a, float *b) {
 #if SWAP_WORDS == 1
     for (; n > 0; n--) {
         int32_t s = *(a++);
-        *(b++) = (float) (((double) INT32_FROM(s))/0x7FFFFFFF);
+        *(b++) = INT32_FROM(s) * (1.0f / (1U << 31));
     }
 #else
     for (; n > 0; n--)
-        *(b++) = (float) (((double) (*(a++)))/0x7FFFFFFF);
+        *(b++) = *(a++) * (1.0f / (1U << 31));
 #endif
 }
 
@@ -115,18 +115,16 @@ void pa_sconv_s16le_from_float32ne(unsigned n, const float *a, int16_t *b) {
 #if SWAP_WORDS == 1
     for (; n > 0; n--) {
         int16_t s;
-        float v = *(a++);
+        float v = *(a++) * (1 << 15);
 
-        v = PA_CLAMP_UNLIKELY(v, -1.0f, 1.f);
-        s = (int16_t) lrintf(v * 0x7FFF);
+        s = (int16_t) PA_CLAMP_UNLIKELY(lrintf(v), -0x8000, 0x7FFF);
         *(b++) = INT16_TO(s);
     }
 #else
     for (; n > 0; n--) {
-        float v = *(a++);
+        float v = *(a++) * (1 << 15);
 
-        v = PA_CLAMP_UNLIKELY(v, -1.0f, 1.f);
-        *(b++) = (int16_t) lrintf(v * 0x7FFF);
+        *(b++) = (int16_t) PA_CLAMP_UNLIKELY(lrintf(v), -0x8000, 0x7FFF);
     }
 #endif
 }
@@ -138,18 +136,16 @@ void pa_sconv_s32le_from_float32ne(unsigned n, const float *a, int32_t *b) {
 #if SWAP_WORDS == 1
     for (; n > 0; n--) {
         int32_t s;
-        float v = *(a++);
+        float v = *(a++) * (1U << 31);
 
-        v = PA_CLAMP_UNLIKELY(v, -1.0f, 1.0f);
-        s = (int32_t) lrint((double) v * (double) 0x7FFFFFFF);
+        s = (int32_t) PA_CLAMP_UNLIKELY(llrintf(v), -0x80000000LL, 0x7FFFFFFFLL);
         *(b++) = INT32_TO(s);
     }
 #else
     for (; n > 0; n--) {
-        float v = *(a++);
+        float v = *(a++) * (1U << 31);
 
-        v = PA_CLAMP_UNLIKELY(v, -1.0f, 1.0f);
-        *(b++) = (int32_t) lrint((double) v * (double) 0x7FFFFFFF);
+        *(b++) = (int32_t) PA_CLAMP_UNLIKELY(llrintf(v), -0x80000000LL, 0x7FFFFFFFLL);
     }
 #endif
 }
@@ -160,7 +156,7 @@ void pa_sconv_s16le_to_float32re(unsigned n, const int16_t *a, float *b) {
 
     for (; n > 0; n--) {
         int16_t s = *(a++);
-        float k = ((float) INT16_FROM(s))/0x7FFF;
+        float k = INT16_FROM(s) * (1.0f / (1 << 15));
         k = PA_FLOAT32_SWAP(k);
         *(b++) = k;
     }
@@ -172,7 +168,7 @@ void pa_sconv_s32le_to_float32re(unsigned n, const int32_t *a, float *b) {
 
     for (; n > 0; n--) {
         int32_t s = *(a++);
-        float k = (float) (((double) INT32_FROM(s))/0x7FFFFFFF);
+        float k = INT32_FROM(s) * (1.0f / (1U << 31));
         k = PA_FLOAT32_SWAP(k);
         *(b++) = k;
     }
@@ -185,9 +181,8 @@ void pa_sconv_s16le_from_float32re(unsigned n, const float *a, int16_t *b) {
     for (; n > 0; n--) {
         int16_t s;
         float v = *(a++);
-        v = PA_FLOAT32_SWAP(v);
-        v = PA_CLAMP_UNLIKELY(v, -1.0f, 1.0f);
-        s = (int16_t) lrintf(v * 0x7FFF);
+        v = PA_FLOAT32_SWAP(v) * (1 << 15);
+        s = (int16_t) PA_CLAMP_UNLIKELY(lrintf(v), -0x8000, 0x7FFF);
         *(b++) = INT16_TO(s);
     }
 }
@@ -199,9 +194,8 @@ void pa_sconv_s32le_from_float32re(unsigned n, const float *a, int32_t *b) {
     for (; n > 0; n--) {
         int32_t s;
         float v = *(a++);
-        v = PA_FLOAT32_SWAP(v);
-        v = PA_CLAMP_UNLIKELY(v, -1.0f, 1.0f);
-        s = (int32_t) lrint((double) v * 0x7FFFFFFF);
+        v = PA_FLOAT32_SWAP(v) * (1U << 31);
+        s = (int32_t) PA_CLAMP_UNLIKELY(llrintf(v), -0x80000000LL, 0x7FFFFFFFLL);
         *(b++) = INT32_TO(s);
     }
 }
@@ -304,9 +298,9 @@ void pa_sconv_s24le_to_float32ne(unsigned n, const uint8_t *a, float *b) {
 
     for (; n > 0; n--) {
         int32_t s = READ24(a) << 8;
-        *b = ((float) s) / 0x7FFFFFFF;
+        *b = s * (1.0f / (1U << 31));
         a += 3;
-        b ++;
+        b++;
     }
 }
 
@@ -316,12 +310,11 @@ void pa_sconv_s24le_from_float32ne(unsigned n, const float *a, uint8_t *b) {
 
     for (; n > 0; n--) {
         int32_t s;
-        float v = *a;
-        v = PA_CLAMP_UNLIKELY(v, -1.0f, 1.0f);
-        s = (int32_t) lrint((double) v * (double) 0x7FFFFFFF);
+        float v = *a * (1U << 31);
+        s = (int32_t) PA_CLAMP_UNLIKELY(llrint(v), -0x80000000LL, 0x7FFFFFFFLL);
         WRITE24(b, ((uint32_t) s) >> 8);
         a++;
-        b+=3;
+        b += 3;
     }
 }
 
@@ -331,10 +324,10 @@ void pa_sconv_s24le_to_float32re(unsigned n, const uint8_t *a, float *b) {
 
     for (; n > 0; n--) {
         int32_t s = READ24(a) << 8;
-        float k = ((float) s) / 0x7FFFFFFF;
+        float k = s * (1.0f / (1U << 31));
         *b = PA_FLOAT32_SWAP(k);
         a += 3;
-        b ++;
+        b++;
     }
 }
 
@@ -345,9 +338,8 @@ void pa_sconv_s24le_from_float32re(unsigned n, const float *a, uint8_t *b) {
     for (; n > 0; n--) {
         int32_t s;
         float v = *a;
-        v = PA_FLOAT32_SWAP(v);
-        v = PA_CLAMP_UNLIKELY(v, -1.0f, 1.0f);
-        s = (int32_t) lrint((double) v * (double) 0x7FFFFFFF);
+        v = PA_FLOAT32_SWAP(v) * (1U << 31);
+        s = (int32_t) PA_CLAMP_UNLIKELY(llrint(v), -0x80000000LL, 0x7FFFFFFFLL);
         WRITE24(b, ((uint32_t) s) >> 8);
         a++;
         b+=3;
@@ -406,9 +398,9 @@ void pa_sconv_s24_32le_to_float32ne(unsigned n, const uint32_t *a, float *b) {
 
     for (; n > 0; n--) {
         int32_t s = (int32_t) (UINT32_FROM(*a) << 8);
-        *b = (float) s / (float) 0x7FFFFFFF;
-        a ++;
-        b ++;
+        *b = s * (1.0f / (1U << 31));
+        a++;
+        b++;
     }
 }
 
@@ -418,10 +410,10 @@ void pa_sconv_s24_32le_to_float32re(unsigned n, const uint32_t *a, float *b) {
 
     for (; n > 0; n--) {
         int32_t s = (int32_t) (UINT32_FROM(*a) << 8);
-        float k = (float) s / (float) 0x7FFFFFFF;
+        float k = s * (1.0f / (1U << 31));
         *b = PA_FLOAT32_SWAP(k);
-        a ++;
-        b ++;
+        a++;
+        b++;
     }
 }
 
@@ -431,9 +423,8 @@ void pa_sconv_s24_32le_from_float32ne(unsigned n, const float *a, uint32_t *b) {
 
     for (; n > 0; n--) {
         int32_t s;
-        float v = *a;
-        v = PA_CLAMP_UNLIKELY(v, -1.0f, 1.0f);
-        s = (int32_t) lrint((double) v * (double) 0x7FFFFFFF);
+        float v = *a * (1U << 31);
+        s = (int32_t) PA_CLAMP_UNLIKELY(llrint(v), -0x80000000LL, 0x7FFFFFFFLL);
         *b = UINT32_TO(((uint32_t) s) >> 8);
         a++;
         b++;
@@ -447,9 +438,8 @@ void pa_sconv_s24_32le_from_float32re(unsigned n, const float *a, uint32_t *b) {
     for (; n > 0; n--) {
         int32_t s;
         float v = *a;
-        v = PA_FLOAT32_SWAP(v);
-        v = PA_CLAMP_UNLIKELY(v, -1.0f, 1.0f);
-        s = (int32_t) lrint((double) v * (double) 0x7FFFFFFF);
+        v = PA_FLOAT32_SWAP(v) * (1U << 31);
+        s = (int32_t) PA_CLAMP_UNLIKELY(llrint(v), -0x80000000LL, 0x7FFFFFFFLL);
         *b = UINT32_TO(((uint32_t) s) >> 8);
         a++;
         b++;
diff --git a/src/pulsecore/sconv_neon.c b/src/pulsecore/sconv_neon.c
index 6fd966d..ddcdcc2 100644
--- a/src/pulsecore/sconv_neon.c
+++ b/src/pulsecore/sconv_neon.c
@@ -36,18 +36,13 @@ static void pa_sconv_s16le_from_f32ne_neon(unsigned n, const float *src, int16_t
         "movs       %[n], %[n], lsr #2      \n\t"
         "beq        2f                      \n\t"
 
-        "vdup.f32   q2, %[plusone]          \n\t"
-        "vneg.f32   q3, q2                  \n\t"
-        "vdup.f32   q4, %[scale]            \n\t"
-        "vdup.u32   q5, %[mask]             \n\t"
+        "vdup.f32   q1, %[scale]            \n\t"
 
         "1:                                 \n\t"
         "vld1.32    {q0}, [%[src]]!         \n\t"
-        "vmin.f32   q0, q0, q2              \n\t" /* clamp */
-        "vmax.f32   q0, q0, q3              \n\t"
-        "vmul.f32   q0, q0, q4              \n\t" /* scale */
-        "vcvt.s32.f32 q0, q0, #16           \n\t" /* narrow */
-        "vrshrn.s32  d0, q0, #16            \n\t"
+        "vmul.f32   q0, q0, q1              \n\t" /* scale */
+        "vcvt.s32.f32 q0, q0, #16           \n\t" /* s32<-f32 as 16:16 fixed-point */
+        "vqrshrn.s32 d0, q0, #16            \n\t" /* shift, round, narrow */
         "subs       %[n], %[n], #1          \n\t"
         "vst1.16    {d0}, [%[dst]]!         \n\t"
         "bgt        1b                      \n\t"
@@ -55,13 +50,13 @@ static void pa_sconv_s16le_from_f32ne_neon(unsigned n, const float *src, int16_t
         "2:                                 \n\t"
 
         : [dst] "+r" (dst), [src] "+r" (src), [n] "+r" (n) /* output operands (or input operands that get modified) */
-        : [plusone] "r" (1.0f), [scale] "r" (32767.0f), [mask] "r" (0x80000000) /* input operands */
-        : "memory", "cc", "q0", "q1", "q2", "q3", "q4", "q5", "q6" /* clobber list */
+        : [scale] "r" (32768.0f) /* input operands */
+        : "memory", "cc", "q0", "q1" /* clobber list */
     );
 
     /* leftovers */
     while (i--) {
-        *dst++ = (int16_t) lrintf(PA_CLAMP_UNLIKELY(*src, -1.0f, 1.0f) * 0x7FFF);
+        *dst++ = (int16_t) PA_CLAMP_UNLIKELY(lrintf(*src * (1 << 15)), -0x8000, 0x7FFF);
         src++;
     }
 }
@@ -69,7 +64,7 @@ static void pa_sconv_s16le_from_f32ne_neon(unsigned n, const float *src, int16_t
 static void pa_sconv_s16le_to_f32ne_neon(unsigned n, const int16_t *src, float *dst) {
     unsigned i = n & 3;
 
-    const float invscale = 1.0f / 0x7FFF;
+    const float invscale = 1.0f / (1 << 15);
 
     __asm__ __volatile__ (
         "movs        %[n], %[n], lsr #2     \n\t"
@@ -79,8 +74,8 @@ static void pa_sconv_s16le_to_f32ne_neon(unsigned n, const int16_t *src, float *
 
         "1:                                 \n\t"
         "vld1.16    {d0}, [%[src]]!         \n\t"
-        "vmovl.s16  q0, d0                  \n\t"
-        "vcvt.f32.s32 q0, q0                \n\t"
+        "vmovl.s16  q0, d0                  \n\t" /* widen */
+        "vcvt.f32.s32 q0, q0                \n\t" /* f32<-s32 */
         "vmul.f32   q0, q0, q1              \n\t"
         "subs       %[n], %[n], #1          \n\t"
         "vst1.32    {q0}, [%[dst]]!         \n\t"
diff --git a/src/pulsecore/sconv_sse.c b/src/pulsecore/sconv_sse.c
index 34b59fa..2f84f5a 100644
--- a/src/pulsecore/sconv_sse.c
+++ b/src/pulsecore/sconv_sse.c
@@ -35,17 +35,13 @@
 
 #if !defined(__APPLE__) && defined (__i386__) || defined (__amd64__)
 
-static const PA_DECLARE_ALIGNED (16, float, one[4]) = { 1.0, 1.0, 1.0, 1.0 };
-static const PA_DECLARE_ALIGNED (16, float, mone[4]) = { -1.0, -1.0, -1.0, -1.0 };
-static const PA_DECLARE_ALIGNED (16, float, scale[4]) = { 0x7fff, 0x7fff, 0x7fff, 0x7fff };
+static const PA_DECLARE_ALIGNED (16, float, scale[4]) = { 0x8000, 0x8000, 0x8000, 0x8000 };
 
 static void pa_sconv_s16le_from_f32ne_sse(unsigned n, const float *a, int16_t *b) {
     pa_reg_x86 temp, i;
 
     __asm__ __volatile__ (
         " movaps %5, %%xmm5             \n\t"
-        " movaps %6, %%xmm6             \n\t"
-        " movaps %7, %%xmm7             \n\t"
         " xor %0, %0                    \n\t"
 
         " mov %4, %1                    \n\t"
@@ -56,12 +52,8 @@ static void pa_sconv_s16le_from_f32ne_sse(unsigned n, const float *a, int16_t *b
         "1:                             \n\t"
         " movups (%q2, %0, 2), %%xmm0   \n\t" /* read 8 floats */
         " movups 16(%q2, %0, 2), %%xmm2 \n\t"
-        " minps  %%xmm5, %%xmm0         \n\t" /* clamp to 1.0 */
-        " minps  %%xmm5, %%xmm2         \n\t"
-        " maxps  %%xmm6, %%xmm0         \n\t" /* clamp to -1.0 */
-        " maxps  %%xmm6, %%xmm2         \n\t"
-        " mulps  %%xmm7, %%xmm0         \n\t" /* *= 0x7fff */
-        " mulps  %%xmm7, %%xmm2         \n\t"
+        " mulps  %%xmm5, %%xmm0         \n\t" /* *= 0x8000 */
+        " mulps  %%xmm5, %%xmm2         \n\t"
 
         " cvtps2pi %%xmm0, %%mm0        \n\t" /* low part to int */
         " cvtps2pi %%xmm2, %%mm2        \n\t"
@@ -73,7 +65,7 @@ static void pa_sconv_s16le_from_f32ne_sse(unsigned n, const float *a, int16_t *b
         " packssdw %%mm1, %%mm0         \n\t" /* pack parts */
         " packssdw %%mm3, %%mm2         \n\t"
         " movq     %%mm0, (%q3, %0)     \n\t"
-        " movq    %%mm2, 8(%q3, %0)     \n\t"
+        " movq     %%mm2, 8(%q3, %0)    \n\t"
 
         " add $16, %0                   \n\t"
         " dec %1                        \n\t"
@@ -82,24 +74,30 @@ static void pa_sconv_s16le_from_f32ne_sse(unsigned n, const float *a, int16_t *b
         "2:                             \n\t"
         " mov %4, %1                    \n\t" /* prepare for leftovers */
         " and $7, %1                    \n\t"
-        " je 4f                         \n\t"
+        " je 5f                         \n\t"
 
         "3:                             \n\t"
         " movss (%q2, %0, 2), %%xmm0    \n\t"
-        " minss  %%xmm5, %%xmm0         \n\t"
-        " maxss  %%xmm6, %%xmm0         \n\t"
-        " mulss  %%xmm7, %%xmm0         \n\t"
+        " mulss  %%xmm5, %%xmm0         \n\t"
+        " cvtss2si %%xmm0, %4           \n\t"
+        " add $0x8000, %4               \n\t" /* check for saturation */
+        " and $~0xffff, %4              \n\t"
         " cvtss2si %%xmm0, %4           \n\t"
-        " movw  %w4, (%q3, %0)          \n\t"
+        " je 4f                         \n\t"
+        " sar $31, %4                   \n\t"
+        " xor $0x7fff, %4               \n\t"
+
+        "4:                             \n\t"
+        " movw  %w4, (%q3, %0)          \n\t" /* store leftover */
         " add $2, %0                    \n\t"
         " dec %1                        \n\t"
         " jne 3b                        \n\t"
 
-        "4:                             \n\t"
+        "5:                             \n\t"
         " emms                          \n\t"
 
         : "=&r" (i), "=&r" (temp)
-        : "r" (a), "r" (b), "r" ((pa_reg_x86)n), "m" (*one), "m" (*mone), "m" (*scale)
+        : "r" (a), "r" (b), "r" ((pa_reg_x86)n), "m" (*scale)
         : "cc", "memory"
     );
 }
@@ -109,8 +107,6 @@ static void pa_sconv_s16le_from_f32ne_sse2(unsigned n, const float *a, int16_t *
 
     __asm__ __volatile__ (
         " movaps %5, %%xmm5             \n\t"
-        " movaps %6, %%xmm6             \n\t"
-        " movaps %7, %%xmm7             \n\t"
         " xor %0, %0                    \n\t"
 
         " mov %4, %1                    \n\t"
@@ -121,12 +117,8 @@ static void pa_sconv_s16le_from_f32ne_sse2(unsigned n, const float *a, int16_t *
         "1:                             \n\t"
         " movups (%q2, %0, 2), %%xmm0   \n\t" /* read 8 floats */
         " movups 16(%q2, %0, 2), %%xmm2 \n\t"
-        " minps  %%xmm5, %%xmm0         \n\t" /* clamp to 1.0 */
-        " minps  %%xmm5, %%xmm2         \n\t"
-        " maxps  %%xmm6, %%xmm0         \n\t" /* clamp to -1.0 */
-        " maxps  %%xmm6, %%xmm2         \n\t"
-        " mulps  %%xmm7, %%xmm0         \n\t" /* *= 0x7fff */
-        " mulps  %%xmm7, %%xmm2         \n\t"
+        " mulps  %%xmm5, %%xmm0         \n\t" /* *= 0x8000 */
+        " mulps  %%xmm5, %%xmm2         \n\t"
 
         " cvtps2dq %%xmm0, %%xmm0       \n\t"
         " cvtps2dq %%xmm2, %%xmm2       \n\t"
@@ -141,23 +133,29 @@ static void pa_sconv_s16le_from_f32ne_sse2(unsigned n, const float *a, int16_t *
         "2:                             \n\t"
         " mov %4, %1                    \n\t" /* prepare for leftovers */
         " and $7, %1                    \n\t"
-        " je 4f                         \n\t"
+        " je 5f                         \n\t"
 
         "3:                             \n\t"
         " movss (%q2, %0, 2), %%xmm0    \n\t"
-        " minss  %%xmm5, %%xmm0         \n\t"
-        " maxss  %%xmm6, %%xmm0         \n\t"
-        " mulss  %%xmm7, %%xmm0         \n\t"
+        " mulss  %%xmm5, %%xmm0         \n\t"
+        " cvtss2si %%xmm0, %4           \n\t"
+        " add $0x8000, %4               \n\t"
+        " and $~0xffff, %4              \n\t" /* check for saturation */
         " cvtss2si %%xmm0, %4           \n\t"
-        " movw  %w4, (%q3, %0)          \n\t"
+        " je 4f                         \n\t"
+        " sar $31, %4                   \n\t"
+        " xor $0x7fff, %4               \n\t"
+
+        "4:                             \n\t"
+        " movw  %w4, (%q3, %0)          \n\t" /* store leftover */
         " add $2, %0                    \n\t"
         " dec %1                        \n\t"
         " jne 3b                        \n\t"
 
-        "4:                             \n\t"
+        "5:                             \n\t"
 
         : "=&r" (i), "=&r" (temp)
-        : "r" (a), "r" (b), "r" ((pa_reg_x86)n), "m" (*one), "m" (*mone), "m" (*scale)
+        : "r" (a), "r" (b), "r" ((pa_reg_x86)n), "m" (*scale)
         : "cc", "memory"
     );
 }
-- 
1.8.1.1



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