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

Daniel Vetter
2019-04-24T20:05:35Z

On Fri, Apr 05, 2019 at 01:14:03PM -0700, Kevin Strasser wrote:
> 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>

btw this broke the build, and someone else got to fix it up for you:

commit 11e10bc575516c56978640fcc697c27f277c660a
Author: Simon Ser <simon.ser@intel.com>
Date: Wed Apr 24 10:01:29 2019 +0300

lib/igt_halffloat: fix compilation with Clang

Cheers, Daniel
> ---
> 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
>
> _______________________________________________
> igt-dev mailing list
> igt-dev@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/igt-dev

--
Daniel Vetter
Software Engineer, Intel Corporation