glsl: Create file to contain software fp64 functions

The following patches will add implementations of various
double-precision operations to this file.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/compiler/glsl/float64.glsl

@@ -0,0 +1,58 @@
+/*
+ * The implementations contained in this file are heavily based on the
+ * implementations found in the Berkeley SoftFloat library. As such, they are
+ * licensed under the same 3-clause BSD license:
+ *
+ * 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.
+*/
+
+#version 430
+#extension GL_ARB_gpu_shader_int64 : enable
+#extension GL_ARB_shader_bit_encoding : enable
+
+#pragma warning(off)
+
+/* Software IEEE floating-point rounding mode.
+ * GLSL spec section "4.7.1 Range and Precision":
+ * The rounding mode cannot be set and is undefined.
+ * But here, we are able to define the rounding mode at the compilation time.
+ */
+#define FLOAT_ROUND_NEAREST_EVEN    0
+#define FLOAT_ROUND_TO_ZERO         1
+#define FLOAT_ROUND_DOWN            2
+#define FLOAT_ROUND_UP              3
+#define FLOAT_ROUNDING_MODE         FLOAT_ROUND_NEAREST_EVEN