FFmpeg
float2half.h
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1 /*
2  * This file is part of FFmpeg.
3  *
4  * FFmpeg is free software; you can redistribute it and/or
5  * modify it under the terms of the GNU Lesser General Public
6  * License as published by the Free Software Foundation; either
7  * version 2.1 of the License, or (at your option) any later version.
8  *
9  * FFmpeg is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12  * Lesser General Public License for more details.
13  *
14  * You should have received a copy of the GNU Lesser General Public
15  * License along with FFmpeg; if not, write to the Free Software
16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
17  */
18 
19 #ifndef AVCODEC_FLOAT2HALF_H
20 #define AVCODEC_FLOAT2HALF_H
21 
22 #include <stdint.h>
23 
24 static void float2half_tables(uint16_t *basetable, uint8_t *shifttable)
25 {
26  for (int i = 0; i < 256; i++) {
27  int e = i - 127;
28 
29  if (e < -24) { // Very small numbers map to zero
30  basetable[i|0x000] = 0x0000;
31  basetable[i|0x100] = 0x8000;
32  shifttable[i|0x000] = 24;
33  shifttable[i|0x100] = 24;
34  } else if (e < -14) { // Small numbers map to denorms
35  basetable[i|0x000] = (0x0400>>(-e-14));
36  basetable[i|0x100] = (0x0400>>(-e-14)) | 0x8000;
37  shifttable[i|0x000] = -e-1;
38  shifttable[i|0x100] = -e-1;
39  } else if (e <= 15) { // Normal numbers just lose precision
40  basetable[i|0x000] = ((e + 15) << 10);
41  basetable[i|0x100] = ((e + 15) << 10) | 0x8000;
42  shifttable[i|0x000] = 13;
43  shifttable[i|0x100] = 13;
44  } else if (e < 128) { // Large numbers map to Infinity
45  basetable[i|0x000] = 0x7C00;
46  basetable[i|0x100] = 0xFC00;
47  shifttable[i|0x000] = 24;
48  shifttable[i|0x100] = 24;
49  } else { // Infinity and NaN's stay Infinity and NaN's
50  basetable[i|0x000] = 0x7C00;
51  basetable[i|0x100] = 0xFC00;
52  shifttable[i|0x000] = 13;
53  shifttable[i|0x100] = 13;
54  }
55  }
56 }
57 
58 static uint16_t float2half(uint32_t f, uint16_t *basetable, uint8_t *shifttable)
59 {
60  uint16_t h;
61 
62  h = basetable[(f >> 23) & 0x1ff] + ((f & 0x007fffff) >> shifttable[(f >> 23) & 0x1ff]);
63 
64  return h;
65 }
66 
67 #endif /* AVCODEC_FLOAT2HALF_H */
f
#define f(width, name)
Definition: cbs_vp9.c:255
float2half
static uint16_t float2half(uint32_t f, uint16_t *basetable, uint8_t *shifttable)
Definition: float2half.h:58
i
int i
Definition: input.c:406
float2half_tables
static void float2half_tables(uint16_t *basetable, uint8_t *shifttable)
Definition: float2half.h:24
h
h
Definition: vp9dsp_template.c:2038