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ab09822b86
Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Fixes: ecd2d2cf46 ("util: Add functions to convert float to/from bfloat16")
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34882>
69 lines
1.4 KiB
C
69 lines
1.4 KiB
C
/*
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* Copyright © 2025 Intel Corporation
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* SPDX-License-Identifier: MIT
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*/
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#pragma once
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#include <assert.h>
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#include <math.h>
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#include <stdint.h>
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#include "u_math.h"
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/* When converting a Float NaN value to BFloat16 it is possible that the
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* significand bits that make the value a NaN will be rounded/truncated off
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* so ensure at least one significand bit is set.
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*/
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static inline uint16_t
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_mesa_float_nan_to_bfloat_bits(union fi x)
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{
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assert(isnan(x.f));
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return x.ui >> 16 | 1 << 6;
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}
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/* Round-towards-zero. */
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static inline uint16_t
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_mesa_float_to_bfloat16_bits_rtz(float f)
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{
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union fi x;
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x.f = f;
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if (isnan(f))
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return _mesa_float_nan_to_bfloat_bits(x);
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return x.ui >> 16;
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}
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/* Round-to-nearest-even. */
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static inline uint16_t
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_mesa_float_to_bfloat16_bits_rte(float f)
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{
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union fi x;
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x.f = f;
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if (isnan(f))
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return _mesa_float_nan_to_bfloat_bits(x);
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/* Use the tail part that is discarded to decide rounding,
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* break the tie with the nearest even.
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*
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* Overflow of the significand value will turn to zero and
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* increment the exponent. If exponent reaches 0xff, the
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* value will correctly end up as +/- Inf.
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*/
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uint32_t result = x.ui >> 16;
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const uint32_t tail = x.ui & 0xffff;
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if (tail > 0x8000 || (tail == 0x8000 && (result & 1) == 1))
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result++;
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return result;
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}
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static inline float
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_mesa_bfloat16_bits_to_float(uint16_t bf)
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{
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union fi x;
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x.ui = bf << 16;
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return x.f;
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}
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