util: add softfloat functions to operate with doubles and floats

Implemented fadd, fsub, fmul and ffma for doubles and ffma for floats,
rounding to zero, using a modified implementation from Berkely
Softfloat 3e Library.

Their implementation correctness has been checked with the Berkeley
TestFloat Release 3e tool for x86_64.

v2:
- Reuse util_last_bit64() in _mesa_count_leading_zeros64()
  implementation (Connor).

v3:
- Add a specific ffma for floats version (Connor).
- Implement the ffma for doubles version (Andres).
- Lots of fixes in fadd, fsub and fmul (Andres).
- Improved documentation (Andres).

v4:
- Added f64 -> f32 conversion function (Andres).
- Added f32 -> f16 RTZ conversion function (Andres).

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Signed-off-by: Andres Gomez <agomez@igalia.com>
Tested-by: Andres Gomez <agomez@igalia.com>
Acked-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>

src/util/Makefile.sources

@@ -56,6 +56,8 @@ MESA_UTIL_FILES := \
 	simple_mtx.h \
 	slab.c \
 	slab.h \
+	softfloat.c \
+	softfloat.h \
 	string_buffer.c \
 	string_buffer.h \
 	strndup.h \

src/util/meson.build

@@ -78,6 +78,8 @@ files_mesa_util = files(
   'simple_mtx.h',
   'slab.c',
   'slab.h',
+  'softfloat.c',
+  'softfloat.h',
   'string_buffer.c',
   'string_buffer.h',
   'strndup.h',

src/util/softfloat.h

@@ -0,0 +1,65 @@
+/*
+ * License for Berkeley SoftFloat Release 3e
+ *
+ * John R. Hauser
+ * 2018 January 20
+ *
+ * The following applies to the whole of SoftFloat Release 3e as well as to
+ * each source file individually.
+ *
+ * Copyright 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018 The Regents of the
+ * University of California.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *  1. Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions, and the following disclaimer.
+ *
+ *  2. Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions, and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ *  3. Neither the name of the University nor the names of its contributors
+ *     may be used to endorse or promote products derived from this software
+ *     without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS "AS IS", AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ARE
+ * DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ *
+ * The functions listed in this file are modified versions of the ones
+ * from the Berkeley SoftFloat 3e Library.
+ */
+
+#ifndef _SOFTFLOAT_H_
+#define _SOFTFLOAT_H_
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+double _mesa_double_add_rtz(double a, double b);
+double _mesa_double_sub_rtz(double a, double b);
+double _mesa_double_mul_rtz(double a, double b);
+double _mesa_double_fma_rtz(double a, double b, double c);
+float _mesa_float_fma_rtz(float a, float b, float c);
+float _mesa_double_to_f32(double x, bool rtz);
+uint16_t _mesa_float_to_half_rtz(float x);
+
+#ifdef __cplusplus
+} /* extern C */
+#endif
+
+#endif  /* _SOFTFLOAT_H */