[igt-dev] [PATCH 1/3] lib: Add halffloat implementation

Kevin Strasser
2019-04-05T20:14:06Z

Probe for and make an API available for tests to use f16c intrinsics to
generate needed fp16 pixel data.

Also import a pure c fp32 <-> fp16 conversion implementation from Mesa
18.3.4, which will act as a fallback when f16c is unavailable.

rfc2:
- Change API to reduce number of function calls (Maarten)

v1:
- Move pragma so AVX code isn't emitted for fallbacks (Ville)
- Change edx to ecx (Ville)

Signed-off-by: Kevin Strasser <kevin.strasser@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
COPYING | 22 +++++
lib/Makefile.sources | 2 +
lib/igt_halffloat.c | 234 +++++++++++++++++++++++++++++++++++++++++++++++++++
lib/igt_halffloat.h | 27 ++++++
lib/igt_x86.c | 9 ++
lib/igt_x86.h | 1 +
lib/meson.build | 1 +
7 files changed, 296 insertions(+)
create mode 100644 lib/igt_halffloat.c
create mode 100644 lib/igt_halffloat.h

diff --git a/COPYING b/COPYING
index 29e0238..0fe6584 100644
--- a/COPYING
+++ b/COPYING
@@ -126,3 +126,25 @@ SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+Copyright (C) 1999-2007 Brian Paul All Rights Reserved.
+Copyright 2015 Philip Taylor <philip@zaynar.co.uk>
+Copyright 2018 Advanced Micro Devices, Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included
+in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.
diff --git a/lib/Makefile.sources b/lib/Makefile.sources
index e00347f..84d14c9 100644
--- a/lib/Makefile.sources
+++ b/lib/Makefile.sources
@@ -32,6 +32,8 @@ lib_source_list = \
igt_gt.h \
igt_gvt.c \
igt_gvt.h \
+ igt_halffloat.c \
+ igt_halffloat.h \
igt_matrix.c \
igt_matrix.h \
igt_primes.c \
diff --git a/lib/igt_halffloat.c b/lib/igt_halffloat.c
new file mode 100644
index 0000000..263b28c
--- /dev/null
+++ b/lib/igt_halffloat.c
@@ -0,0 +1,234 @@
+/*
+ * Copyright (C) 1999-2007 Brian Paul All Rights Reserved.
+ * Copyright 2015 Philip Taylor <philip@zaynar.co.uk>
+ * Copyright 2018 Advanced Micro Devices, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <assert.h>
+#include <math.h>
+
+#include "igt_halffloat.h"
+#include "igt_x86.h"
+
+typedef union { float f; int32_t i; uint32_t u; } fi_type;
+
+/**
+ * Convert a 4-byte float to a 2-byte half float.
+ *
+ * Not all float32 values can be represented exactly as a float16 value. We
+ * round such intermediate float32 values to the nearest float16. When the
+ * float32 lies exactly between to float16 values, we round to the one with
+ * an even mantissa.
+ *
+ * This rounding behavior has several benefits:
+ * - It has no sign bias.
+ *
+ * - It reproduces the behavior of real hardware: opcode F32TO16 in Intel's
+ * GPU ISA.
+ *
+ * - By reproducing the behavior of the GPU (at least on Intel hardware),
+ * compile-time evaluation of constant packHalf2x16 GLSL expressions will
+ * result in the same value as if the expression were executed on the GPU.
+ */
+static inline uint16_t _float_to_half(float val)
+{
+ const fi_type fi = {val};
+ const int flt_m = fi.i & 0x7fffff;
+ const int flt_e = (fi.i >> 23) & 0xff;
+ const int flt_s = (fi.i >> 31) & 0x1;
+ int s, e, m = 0;
+ uint16_t result;
+
+ /* sign bit */
+ s = flt_s;
+
+ /* handle special cases */
+ if ((flt_e == 0) && (flt_m == 0)) {
+ /* zero */
+ /* m = 0; - already set */
+ e = 0;
+ } else if ((flt_e == 0) && (flt_m != 0)) {
+ /* denorm -- denorm float maps to 0 half */
+ /* m = 0; - already set */
+ e = 0;
+ } else if ((flt_e == 0xff) && (flt_m == 0)) {
+ /* infinity */
+ /* m = 0; - already set */
+ e = 31;
+ } else if ((flt_e == 0xff) && (flt_m != 0)) {
+ /* NaN */
+ m = 1;
+ e = 31;
+ } else {
+ /* regular number */
+ const int new_exp = flt_e - 127;
+ if (new_exp < -14) {
+ /* The float32 lies in the range (0.0, min_normal16) and
+ * is rounded to a nearby float16 value. The result will
+ * be either zero, subnormal, or normal.
+ */
+ e = 0;
+ m = lrintf((1 << 24) * fabsf(fi.f));
+ } else if (new_exp > 15) {
+ /* map this value to infinity */
+ /* m = 0; - already set */
+ e = 31;
+ } else {
+ /* The float32 lies in the range
+ * [min_normal16, max_normal16 + max_step16)
+ * and is rounded to a nearby float16 value. The result
+ * will be either normal or infinite.
+ */
+ e = new_exp + 15;
+ m = lrintf(flt_m / (float)(1 << 13));
+ }
+ }
+
+ assert(0 <= m && m <= 1024);
+ if (m == 1024) {
+ /* The float32 was rounded upwards into the range of the next
+ * exponent, so bump the exponent. This correctly handles the
+ * case where f32 should be rounded up to float16 infinity.
+ */
+ ++e;
+ m = 0;
+ }
+
+ result = (s << 15) | (e << 10) | m;
+ return result;
+}
+
+/**
+ * Convert a 2-byte half float to a 4-byte float.
+ * Based on code from:
+ * http://www.opengl.org/discussion_boards/ubb/Forum3/HTML/008786.html
+ */
+static inline float _half_to_float(uint16_t val)
+{
+ /* XXX could also use a 64K-entry lookup table */
+ const int m = val & 0x3ff;
+ const int e = (val >> 10) & 0x1f;
+ const int s = (val >> 15) & 0x1;
+ int flt_m, flt_e, flt_s;
+ fi_type fi;
+
+ /* sign bit */
+ flt_s = s;
+
+ /* handle special cases */
+ if ((e == 0) && (m == 0)) {
+ /* zero */
+ flt_m = 0;
+ flt_e = 0;
+ } else if ((e == 0) && (m != 0)) {
+ /* denorm -- denorm half will fit in non-denorm single */
+ const float half_denorm = 1.0f / 16384.0f; /* 2^-14 */
+ float mantissa = ((float) (m)) / 1024.0f;
+ float sign = s ? -1.0f : 1.0f;
+ return sign * mantissa * half_denorm;
+ } else if ((e == 31) && (m == 0)) {
+ /* infinity */
+ flt_e = 0xff;
+ flt_m = 0;
+ } else if ((e == 31) && (m != 0)) {
+ /* NaN */
+ flt_e = 0xff;
+ flt_m = 1;
+ } else {
+ /* regular */
+ flt_e = e + 112;
+ flt_m = m << 13;
+ }
+
+ fi.i = (flt_s << 31) | (flt_e << 23) | flt_m;
+ return fi.f;
+}
+
+#if defined(__x86_64__) && !defined(__clang__)
+#pragma GCC push_options
+#pragma GCC target("f16c")
+
+#include <immintrin.h>
+
+static void float_to_half_f16c(const float *f, uint16_t *h, unsigned int num)
+{
+ for (int i = 0; i < num; i++)
+ h[i] = _cvtss_sh(f[i], 0);
+}
+
+static void half_to_float_f16c(const uint16_t *h, float *f, unsigned int num)
+{
+ for (int i = 0; i < num; i++)
+ f[i] = _cvtsh_ss(h[i]);
+}
+
+#pragma GCC pop_options
+
+static void float_to_half(const float *f, uint16_t *h, unsigned int num)
+{
+ for (int i = 0; i < num; i++)
+ h[i] = _float_to_half(f[i]);
+}
+
+static void half_to_float(const uint16_t *h, float *f, unsigned int num)
+{
+ for (int i = 0; i < num; i++)
+ f[i] = _half_to_float(h[i]);
+}
+
+static void (*resolve_float_to_half(void))(const float *f, uint16_t *h, unsigned int num)
+{
+ if (igt_x86_features() & F16C)
+ return float_to_half_f16c;
+
+ return float_to_half;
+}
+
+void igt_float_to_half(const float *f, uint16_t *h, unsigned int num)
+ __attribute__((ifunc("resolve_float_to_half")));
+
+static void (*resolve_half_to_float(void))(const uint16_t *h, float *f, unsigned int num)
+{
+ if (igt_x86_features() & F16C)
+ return half_to_float_f16c;
+
+ return half_to_float;
+}
+
+void igt_half_to_float(const uint16_t *h, float *f, unsigned int num)
+ __attribute__((ifunc("resolve_half_to_float")));
+
+#else
+
+void igt_float_to_half(const float *f, uint16_t *h, unsigned int num)
+{
+ for (int i = 0; i < num; i++)
+ h[i] = _float_to_half(f[i]);
+}
+
+float igt_half_to_float(const uint16_t *h, float *f, unsigned int num)
+{
+ for (int i = 0; i < num; i++)
+ f[i] = _half_to_float(h[i]);
+}
+
+#endif
+
diff --git a/lib/igt_halffloat.h b/lib/igt_halffloat.h
new file mode 100644
index 0000000..8db448a
--- /dev/null
+++ b/lib/igt_halffloat.h
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 1999-2007 Brian Paul All Rights Reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <stdint.h>
+
+void igt_float_to_half(const float *f, uint16_t *h, unsigned int num);
+void igt_half_to_float(const uint16_t *h, float *f, unsigned int num);
+
diff --git a/lib/igt_x86.c b/lib/igt_x86.c
index 88e514d..6ac700d 100644
--- a/lib/igt_x86.c
+++ b/lib/igt_x86.c
@@ -88,6 +88,10 @@
#define bit_AVX (1 << 28)
#endif

+#ifndef bit_F16C
+#define bit_F16C (1 << 29)
+#endif
+
#ifndef bit_AVX2
#define bit_AVX2 (1<<5)
#endif
@@ -138,6 +142,9 @@ unsigned igt_x86_features(void)

if (edx & bit_SSE2)
features |= SSE2;
+
+ if (ecx & bit_F16C)
+ features |= F16C;
}

if (max >= 7) {
@@ -174,6 +181,8 @@ char *igt_x86_features_to_string(unsigned features, char *line)
line += sprintf(line, ", avx");
if (features & AVX2)
line += sprintf(line, ", avx2");
+ if (features & F16C)
+ line += sprintf(line, ", f16c");

(void)line;

diff --git a/lib/igt_x86.h b/lib/igt_x86.h
index d4f8c34..c7b84de 100644
--- a/lib/igt_x86.h
+++ b/lib/igt_x86.h
@@ -39,6 +39,7 @@
#define SSE4_2 0x40
#define AVX 0x80
#define AVX2 0x100
+#define F16C 0x200

#if defined(__x86_64__) || defined(__i386__)
unsigned igt_x86_features(void);
diff --git a/lib/meson.build b/lib/meson.build
index 89de06e..a12a8f9 100644
--- a/lib/meson.build
+++ b/lib/meson.build
@@ -12,6 +12,7 @@ lib_sources = [
'igt_gpu_power.c',
'igt_gt.c',
'igt_gvt.c',
+ 'igt_halffloat.c',
'igt_matrix.c',
'igt_perf.c',
'igt_primes.c',
--
2.7.4