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918234ce80
After closely analyzing Google Brain codebases, we decided that flushing to zero was the wrong thing to do. Intel and AMD probably designed their microprocessors to always flush to zero for the wrong reasons. It should have been made conditional on FTZ being set in MXCSR like other opcodes. See ggerganov/llama.cpp#7843
71 lines
1.6 KiB
C
71 lines
1.6 KiB
C
#ifndef BF16_h
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#define BF16_h
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#include <stdint.h>
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/**
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* Converts brain16 to float32.
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*
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* The bfloat16 floating point format has the following structure:
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*
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* ┌sign
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* │
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* │ ┌exponent
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* │ │
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* │ │ ┌mantissa
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* │ │ │
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* │┌──┴───┐┌─┴───┐
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* 0b0000000000000000 brain16
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*
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* Since bf16 has the same number of exponent bits as a 32bit float,
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* encoding and decoding numbers becomes relatively straightforward.
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*
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* ┌sign
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* │
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* │ ┌exponent
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* │ │
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* │ │ ┌mantissa
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* │ │ │
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* │┌──┴───┐┌─┴───────────────────┐
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* 0b00000000000000000000000000000000 IEEE binary32
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*
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* For comparison, the standard fp16 format has fewer exponent bits.
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*
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* ┌sign
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* │
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* │ ┌exponent
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* │ │
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* │ │ ┌mantissa
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* │ │ │
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* │┌─┴─┐┌─┴──────┐
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* 0b0000000000000000 IEEE binary16
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*
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* @see IEEE 754-2008
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*/
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static inline float from_brain(uint16_t h) {
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union {
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float f;
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uint32_t i;
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} u;
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u.i = (uint32_t)h << 16;
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return u.f;
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}
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/**
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* Converts float32 to brain16.
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*/
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static inline uint16_t to_brain(float s) {
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uint16_t h;
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union {
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float f;
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uint32_t i;
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} u;
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u.f = s;
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if ((u.i & 0x7fffffff) > 0x7f800000) { /* nan */
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h = (u.i >> 16) | 64; /* force to quiet */
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return h;
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}
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return (u.i + (0x7fff + ((u.i >> 16) & 1))) >> 16;
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}
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#endif
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