[Mesa-dev] [PATCH 12/28] util: add fp64 -> fp32 conversion support for RTNE and RTZ rounding modes
Samuel Iglesias Gonsálvez
siglesias at igalia.com
Wed Dec 5 15:55:27 UTC 2018
Signed-off-by: Samuel Iglesias Gonsálvez <siglesias at igalia.com>
---
src/util/Makefile.sources | 2 +
src/util/double.c | 197 ++++++++++++++++++++++++++++++++++++++
src/util/double.h | 46 +++++++++
src/util/meson.build | 2 +
4 files changed, 247 insertions(+)
create mode 100644 src/util/double.c
create mode 100644 src/util/double.h
diff --git a/src/util/Makefile.sources b/src/util/Makefile.sources
index f09b89b3be5..1b998bf26c4 100644
--- a/src/util/Makefile.sources
+++ b/src/util/Makefile.sources
@@ -11,6 +11,8 @@ MESA_UTIL_FILES := \
debug.h \
disk_cache.c \
disk_cache.h \
+ double.c \
+ double.h \
fast_idiv_by_const.c \
fast_idiv_by_const.h \
format_r11g11b10f.h \
diff --git a/src/util/double.c b/src/util/double.c
new file mode 100644
index 00000000000..61f23e3b57b
--- /dev/null
+++ b/src/util/double.c
@@ -0,0 +1,197 @@
+/*
+ * Mesa 3-D graphics library
+ *
+ * Copyright (C) 2018 Intel Corporation
+ *
+ * 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 <stdio.h>
+#include <assert.h>
+#include <math.h>
+#include <string.h>
+
+#include "rounding.h"
+#include "double.h"
+
+
+
+
+typedef union { double f; int64_t i; uint64_t u; } fi_type;
+
+/**
+ * Convert a 8-byte double to a 4-byte float.
+ *
+ * Not all float64 values can be represented exactly as a float32 value. We
+ * round such intermediate float64 values to the nearest float32. When the
+ * float64 lies exactly between two float32 values, we round to the one with
+ * an even mantissa.
+ */
+
+float
+_mesa_double_to_float(double val)
+{
+ const fi_type fi = {val};
+ const int64_t flt_m = fi.i & 0x0fffffffffffff;
+ const int64_t flt_e = (fi.i >> 52) & 0x7ff;
+ const int64_t flt_s = (fi.i >> 63) & 0x1;
+ int s, e, m = 0;
+ float 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 float64 maps to 0 */
+ /* m = 0; - already set */
+ e = 0;
+ }
+ else if ((flt_e == 0x7ff) && (flt_m == 0)) {
+ /* infinity */
+ /* m = 0; - already set */
+ e = 255;
+ }
+ else if ((flt_e == 0x7ff) && (flt_m != 0)) {
+ /* NaN */
+ m = 1;
+ e = 255;
+ }
+ else {
+ /* regular number */
+ const int new_exp = flt_e - 1023;
+ if (new_exp < -126) {
+ /* The float64 lies in the range (0.0, min_normal32) and is rounded
+ * to a nearby float32 value. The result will be either zero, subnormal,
+ * or normal.
+ */
+ e = 0;
+ m = _mesa_lroundeven(((double)((uint64_t)1 << 54)) * fabs(fi.f));
+ }
+ else if (new_exp > 127) {
+ /* map this value to infinity */
+ /* m = 0; - already set */
+ e = 255;
+ }
+ else {
+ /* The float64 lies in the range
+ * [min_normal32, max_normal32 + max_step32)
+ * and is rounded to a nearby float32 value. The result will be
+ * either normal or infinite.
+ */
+ e = new_exp + 127;
+ m = _mesa_lroundeven((double)flt_m / (double) (1 << 29));
+ }
+ }
+
+ assert(0 <= m && m <= (1 << 23));
+ if (m == (1 << 23)) {
+ /* The float64 was rounded upwards into the range of the next exponent,
+ * so bump the exponent. This correctly handles the case where f64
+ * should be rounded up to float32 infinity.
+ */
+ ++e;
+ m = 0;
+ }
+
+ unsigned result_int = (s << 31) | (e << 23) | m;
+ memcpy(&result, &result_int, sizeof(float));
+ return result;
+}
+
+float
+_mesa_double_to_float_rtz(double val)
+{
+ const fi_type fi = {val};
+ const int64_t flt_m = fi.i & 0x0fffffffffffff;
+ const int64_t flt_e = (fi.i >> 52) & 0x7ff;
+ const int64_t flt_s = (fi.i >> 63) & 0x1;
+ int s, e, m = 0;
+ float 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 float64 maps to 0 */
+ /* m = 0; - already set */
+ e = 0;
+ }
+ else if ((flt_e == 0xff) && (flt_m == 0)) {
+ /* infinity */
+ /* m = 0; - already set */
+ e = 255;
+ }
+ else if ((flt_e == 0xff) && (flt_m != 0)) {
+ /* NaN */
+ m = 1;
+ e = 255;
+ }
+ else {
+ /* regular number */
+ const int new_exp = flt_e - 1023;
+ if (new_exp < -126) {
+ /* The float64 lies in the range (0.0, min_normal32) and is rounded
+ * to a nearby float32 value. The result will be either zero, subnormal,
+ * or normal.
+ */
+ e = 0;
+ m = trunc((double)((uint64_t)1 << 54) * fabs(fi.f));
+ }
+ else if (new_exp > 127) {
+ /* map this value to infinity */
+ /* m = 0; - already set */
+ e = 255;
+ }
+ else {
+ /* The float64 lies in the range
+ * [min_normal32, max_normal32 + max_step32)
+ * and is rounded to a nearby float32 value. The result will be
+ * either normal or infinite.
+ */
+ e = new_exp + 127;
+ m = trunc((double)flt_m / (double) (1 << 29));
+ }
+ }
+
+ assert(0 <= m && m <= (1 << 23));
+ if (m == (1 << 23)) {
+ /* The float64 was rounded upwards into the range of the next exponent,
+ * so bump the exponent. This correctly handles the case where f64
+ * should be rounded up to float32 infinity.
+ */
+ ++e;
+ m = 0;
+ }
+
+ unsigned result_int = (s << 31) | (e << 23) | m;
+ memcpy(&result, &result_int, sizeof(float));
+ return result;
+}
diff --git a/src/util/double.h b/src/util/double.h
new file mode 100644
index 00000000000..0314c8ea0b5
--- /dev/null
+++ b/src/util/double.h
@@ -0,0 +1,46 @@
+/*
+ * Mesa 3-D graphics library
+ *
+ * Copyright (C) 2018 Intel Corporation
+ *
+ * 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.
+ */
+
+#ifndef _DOUBLE_H_
+#define _DOUBLE_H_
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+float _mesa_double_to_float(double val);
+float _mesa_double_to_float_rtz(double val);
+
+static inline float
+_mesa_double_to_float_rtne(double val)
+{
+ return _mesa_double_to_float(val);
+}
+
+#ifdef __cplusplus
+} /* extern C */
+#endif
+
+#endif /* _DOUBLE_H_ */
diff --git a/src/util/meson.build b/src/util/meson.build
index 397c2228129..23371ef2742 100644
--- a/src/util/meson.build
+++ b/src/util/meson.build
@@ -35,6 +35,8 @@ files_mesa_util = files(
'debug.h',
'disk_cache.c',
'disk_cache.h',
+ 'double.c',
+ 'double.h',
'fast_idiv_by_const.c',
'fast_idiv_by_const.h',
'format_r11g11b10f.h',
--
2.19.1
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