mirror of https://gitlab.freedesktop.org/mesa/mesa
66 lines
1.6 KiB
C
66 lines
1.6 KiB
C
/*
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* Copyright 2021 Alyssa Rosenzweig
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* SPDX-License-Identifier: MIT
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*/
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#ifndef __AGX_MINIFLOAT_H_
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#define __AGX_MINIFLOAT_H_
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#include <math.h>
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#include "util/macros.h"
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/* AGX includes an 8-bit floating-point format for small dyadic immediates,
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* consisting of 3 bits for the exponent, 4 bits for the mantissa, and 1-bit
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* for sign, in the usual order. Zero exponent has special handling. */
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static inline float
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agx_minifloat_decode(uint8_t imm)
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{
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float sign = (imm & 0x80) ? -1.0 : 1.0;
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signed exp = (imm & 0x70) >> 4;
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unsigned mantissa = (imm & 0xF);
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if (exp)
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return ldexpf(sign * (float)(mantissa | 0x10), exp - 7);
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else
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return ldexpf(sign * ((float)mantissa), -6);
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}
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/* Encodes a float. Results are only valid if the float can be represented
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* exactly, if not the result of this function is UNDEFINED. However, it is
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* guaranteed that this function will not crash on out-of-spec inputs, so it is
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* safe to call on any input. signbit() is used to ensure -0.0 is handled
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* correctly.
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*/
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static inline uint8_t
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agx_minifloat_encode(float f)
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{
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unsigned sign = signbit(f) ? 0x80 : 0;
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f = fabsf(f);
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/* frac is in [0.5, 1) and f = frac * 2^exp */
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int exp = 0;
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float frac = frexpf(f, &exp);
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if (f >= 0.25) {
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unsigned mantissa = (frac * 32.0);
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exp -= 5; /* 2^5 = 32 */
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exp = CLAMP(exp + 7, 0, 7);
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return sign | (exp << 4) | (mantissa & 0xF);
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} else {
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unsigned mantissa = (f * 64.0f);
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return sign | mantissa;
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}
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}
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static inline bool
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agx_minifloat_exact(float f)
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{
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float f_ = agx_minifloat_decode(agx_minifloat_encode(f));
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return memcmp(&f, &f_, sizeof(float)) == 0;
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}
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#endif
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