1 /*
2 * Copyright (C) 2021 Alyssa Rosenzweig <alyssa@rosenzweig.io>
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
21 * SOFTWARE.
22 */
23
24 #ifndef __AGX_MINIFLOAT_H_
25 #define __AGX_MINIFLOAT_H_
26
27 #include <math.h>
28 #include "util/macros.h"
29
30 /* AGX includes an 8-bit floating-point format for small dyadic immediates,
31 * consisting of 3 bits for the exponent, 4 bits for the mantissa, and 1-bit
32 * for sign, in the usual order. Zero exponent has special handling. */
33
34 static inline float
agx_minifloat_decode(uint8_t imm)35 agx_minifloat_decode(uint8_t imm)
36 {
37 float sign = (imm & 0x80) ? -1.0 : 1.0;
38 signed exp = (imm & 0x70) >> 4;
39 unsigned mantissa = (imm & 0xF);
40
41 if (exp)
42 return ldexpf(sign * (float) (mantissa | 0x10), exp - 7);
43 else
44 return ldexpf(sign * ((float) mantissa), -6);
45 }
46
47 /* Encodes a float. Results are only valid if the float can be represented
48 * exactly, if not the result of this function is UNDEFINED. signbit() is used
49 * to ensure -0.0 is handled correctly. */
50
51 static inline uint8_t
agx_minifloat_encode(float f)52 agx_minifloat_encode(float f)
53 {
54 unsigned sign = signbit(f) ? 0x80 : 0;
55 f = fabsf(f);
56
57 /* frac is in [0.5, 1) and f = frac * 2^exp */
58 int exp = 0;
59 float frac = frexpf(f, &exp);
60
61 if (f >= 0.25) {
62 unsigned mantissa = (frac * 32.0);
63 exp -= 5; /* 2^5 = 32 */
64 exp = CLAMP(exp + 7, 0, 7);
65
66 assert(mantissa >= 0x10 && mantissa < 0x20);
67 assert(exp >= 1);
68
69 return sign | (exp << 4) | (mantissa & 0xF);
70 } else {
71 unsigned mantissa = (f * 64.0f);
72 assert(mantissa < 0x10);
73
74 return sign | mantissa;
75 }
76 }
77
78 static inline bool
agx_minifloat_exact(float f)79 agx_minifloat_exact(float f)
80 {
81 float f_ = agx_minifloat_decode(agx_minifloat_encode(f));
82 return memcmp(&f, &f_, sizeof(float)) == 0;
83 }
84
85 #endif
86