gallium/util: pregenerate half float tables

This solution avoids the issue of how to run the initializers and
also allows those pages (and the parts of them in processor caches)
to be shared between multiple processes.

The drawback is slightly higher library size.

1 files changed, 179 insertions, 0 deletions

diff --git a/src/gallium/auxiliary/util/u_half.py b/src/gallium/auxiliary/util/u_half.py
new file mode 100644
index 0000000000..a92f758750
--- /dev/null
+++ b/src/gallium/auxiliary/util/u_half.py
@@ -0,0 +1,179 @@
+# Copyright 2010 Luca Barbieri
+#
+# 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 (including the
+# next paragraph) 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 COPYRIGHT OWNER(S) AND/OR ITS SUPPLIERS 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.
+#
+# *************************************************************************
+
+# The code is a reimplementation of the algorithm in
+#  www.fox-toolkit.org/ftp/fasthalffloatconversion.pdf
+# "Fast Half Float Conversions" by Jeroen van der Zijp, Nov 2008
+#
+# The table contents have been slightly changed so that the exponent
+# bias is now in the exponent table instead of the mantissa table (mostly
+# for cosmetic reasons, and because it theoretically allows a variant
+# that flushes denormal to zero but uses a mantissa table with 24-bit
+# entries).
+#
+# The tables are also constructed slightly differently.
+#
+
+# Note that using a 64K * 4 table is a terrible idea since it will not fit
+# in the L1 cache and will massively pollute the L2 cache as well
+#
+# These should instead fit in the L1 cache.
+#
+# TODO: we could use a denormal bias table instead of the mantissa/offset
+# tables: this would reduce the L1 cache usage from 8704 to 2304 bytes
+# but would involve more computation
+#
+# Note however that if denormals are never encountered, the L1 cache usage
+# is only about 4608 bytes anyway.
+
+table_index = None
+table_length = None
+
+def begin(t, n, l):
+	global table_length
+	global table_index
+	table_index = 0
+	table_length = l
+	print
+	print t + " " + n + "[" + str(l) + "] = {"
+
+def value(v):
+	global table_index
+	table_index += 1
+	print "\t" + hex(v) + ","
+
+def end():
+	global table_length
+	global table_index
+	print "};"
+	assert table_index == table_length
+
+print "/* This file is autogenerated by u_half.py. Do not edit directly. */"
+print "#include \"util/u_half.h\""
+
+begin("uint32_t", "util_half_to_float_mantissa_table", 2048)
+# zero
+value(0)
+
+# denormals
+for i in xrange(1, 1024):
+	m = i << 13
+	e = 0
+
+	# normalize number
+	while (m & 0x00800000) == 0:
+		e -= 0x00800000;
+		m <<= 1;
+
+	m &= ~0x00800000;
+	e += 0x38800000;
+	value(m | e)
+
+# normals
+for i in xrange(1024, 2048):
+	value((i - 1024) << 13)
+end()
+
+begin("uint32_t", "util_half_to_float_exponent_table", 64)
+# positive zero or denormals
+value(0)
+
+# positive numbers
+for i in xrange(1, 31):
+	value(0x38000000 + (i << 23))
+
+# positive infinity/NaN
+value(0x7f800000)
+
+# negative zero or denormals
+value(0x80000000)
+
+# negative numbers
+for i in range(33, 63):
+	value(0xb8000000 + ((i - 32) << 23))
+
+# negative infinity/NaN
+value(0xff800000)
+end()
+
+begin("uint32_t", "util_half_to_float_offset_table", 64)
+# positive zero or denormals
+value(0)
+
+# positive normals
+for i in range(1, 32):
+	value(1024)
+
+# negative zero or denormals
+value(0)
+
+# negative normals
+for i in xrange(33, 64):
+	value(1024)
+end()
+
+begin("uint16_t", "util_float_to_half_base_table", 512)
+for sign in (0, 0x8000):
+	# very small numbers mapping to zero
+	for i in xrange(-127, -24):
+		value(sign | 0)
+
+	# small numbers mapping to denormals
+	for i in xrange(-24, -14):
+		value(sign | (0x400 >> (-14 -i)))
+
+	# normal numbers
+	for i in xrange(-14, 16):
+		value(sign | ((i + 15) << 10))
+
+	# large numbers mapping to infinity
+	for i in xrange(16, 128):
+		value(sign | 0x7c00)
+
+	# infinity and NaNs
+	value(sign | 0x7c00)
+end()
+
+begin("uint8_t", "util_float_to_half_shift_table", 512)
+for sign in (0, 0x8000):
+	# very small numbers mapping to zero
+	for i in xrange(-127, -24):
+		value(24)
+
+	# small numbers mapping to denormals
+	for i in xrange(-24, -14):
+		value(-1 - i)
+
+	# normal numbers
+	for i in xrange(-14, 16):
+		value(13)
+
+	# large numbers mapping to infinity
+	for i in xrange(16, 128):
+		value(24)
+
+	# infinity and NaNs
+	value(13)
+end()
+