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/*
* 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.
*/
#include "util/u_half.h"
#include "util/u_init.h"
uint32_t util_half_to_float_mantissa_table[2048];
uint32_t util_half_to_float_exponent_table[64];
uint32_t util_half_to_float_offset_table[64];
uint16_t util_float_to_half_base_table[512];
uint8_t util_float_to_half_shift_table[512];
boolean util_half_inited;
void
util_half_do_init(void)
{
int i;
/* zero */
util_half_to_float_mantissa_table[0] = 0;
/* denormals */
for(i = 1; i < 1024; ++i)
{
unsigned int m = i << 13;
unsigned int e = 0;
/* Normalize number */
while(!(m & 0x00800000))
{
e -= 0x00800000;
m <<= 1;
}
m &= ~0x00800000;
e += 0x38800000;
util_half_to_float_mantissa_table[i] = m | e;
}
/* normals */
for(i = 1024; i < 2048; ++i)
util_half_to_float_mantissa_table[i] = ((i - 1024) << 13);
/* positive zero or denormals */
util_half_to_float_exponent_table[0] = 0;
/* positive numbers */
for(i = 1; i <= 30; ++i)
util_half_to_float_exponent_table[i] = 0x38000000 + (i << 23);
/* positive infinity/NaN */
util_half_to_float_exponent_table[31] = 0x7f800000;
/* negative zero or denormals */
util_half_to_float_exponent_table[32] = 0x80000000;
/* negative numbers */
for(i = 33; i <= 62; ++i)
util_half_to_float_exponent_table[i] = 0xb8000000 + ((i - 32) << 23);
/* negative infinity/NaN */
util_half_to_float_exponent_table[63] = 0xff800000;
/* positive zero or denormals */
util_half_to_float_offset_table[0] = 0;
/* positive normals */
for(i = 1; i < 32; ++i)
util_half_to_float_offset_table[i] = 1024;
/* negative zero or denormals */
util_half_to_float_offset_table[32] = 0;
/* negative normals */
for(i = 33; i < 64; ++i)
util_half_to_float_offset_table[i] = 1024;
/* very small numbers mapping to zero */
for(i = -127; i < -24; ++i)
{
util_float_to_half_base_table[127 + i] = 0;
util_float_to_half_shift_table[127 + i] = 24;
}
/* small numbers mapping to denormals */
for(i = -24; i < -14; ++i)
{
util_float_to_half_base_table[127 + i] = 0x0400 >> (-14 - i);
util_float_to_half_shift_table[127 + i] = -i - 1;
}
/* normal numbers */
for(i = -14; i < 16; ++i)
{
util_float_to_half_base_table[127 + i] = (i + 15) << 10;
util_float_to_half_shift_table[127 + i] = 13;
}
/* large numbers mapping to infinity */
for(i = 16; i < 128; ++i)
{
util_float_to_half_base_table[127 + i] = 0x7c00;
util_float_to_half_shift_table[127 + i] = 24;
}
/* infinity and NaNs */
util_float_to_half_base_table[255] = 0x7c00;
util_float_to_half_shift_table[255] = 13;
/* negative numbers */
for(i = 0; i < 256; ++i)
{
util_float_to_half_base_table[256 + i] = util_float_to_half_base_table[i] | 0x8000;
util_float_to_half_shift_table[256 + i] = util_float_to_half_shift_table[i];
}
}
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