Eyck Jentzsch
dcaf5467e8
(http://www.jhauser.us/arithmetic/SoftFloat.html) with RISCV specialization and cmake build
172 lines
6.4 KiB
C
172 lines
6.4 KiB
C
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/*============================================================================
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This C source file is part of the SoftFloat IEEE Floating-Point Arithmetic
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Package, Release 3e, by John R. Hauser.
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Copyright 2011, 2012, 2013, 2014, 2015, 2016 The Regents of the University of
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California. All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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1. Redistributions of source code must retain the above copyright notice,
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this list of conditions, and the following disclaimer.
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2. Redistributions in binary form must reproduce the above copyright notice,
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this list of conditions, and the following disclaimer in the documentation
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and/or other materials provided with the distribution.
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3. Neither the name of the University nor the names of its contributors may
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be used to endorse or promote products derived from this software without
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specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS "AS IS", AND ANY
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EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ARE
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DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
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DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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=============================================================================*/
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#include <stdbool.h>
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#include <stdint.h>
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#include "platform.h"
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#include "internals.h"
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#include "specialize.h"
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#include "softfloat.h"
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float16_t f16_rem( float16_t a, float16_t b )
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{
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union ui16_f16 uA;
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uint_fast16_t uiA;
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bool signA;
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int_fast8_t expA;
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uint_fast16_t sigA;
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union ui16_f16 uB;
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uint_fast16_t uiB;
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int_fast8_t expB;
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uint_fast16_t sigB;
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struct exp8_sig16 normExpSig;
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uint16_t rem;
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int_fast8_t expDiff;
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uint_fast16_t q;
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uint32_t recip32, q32;
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uint16_t altRem, meanRem;
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bool signRem;
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uint_fast16_t uiZ;
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union ui16_f16 uZ;
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/*------------------------------------------------------------------------
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*------------------------------------------------------------------------*/
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uA.f = a;
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uiA = uA.ui;
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signA = signF16UI( uiA );
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expA = expF16UI( uiA );
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sigA = fracF16UI( uiA );
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uB.f = b;
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uiB = uB.ui;
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expB = expF16UI( uiB );
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sigB = fracF16UI( uiB );
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/*------------------------------------------------------------------------
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*------------------------------------------------------------------------*/
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if ( expA == 0x1F ) {
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if ( sigA || ((expB == 0x1F) && sigB) ) goto propagateNaN;
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goto invalid;
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}
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if ( expB == 0x1F ) {
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if ( sigB ) goto propagateNaN;
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return a;
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}
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/*------------------------------------------------------------------------
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*------------------------------------------------------------------------*/
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if ( ! expB ) {
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if ( ! sigB ) goto invalid;
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normExpSig = softfloat_normSubnormalF16Sig( sigB );
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expB = normExpSig.exp;
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sigB = normExpSig.sig;
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}
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if ( ! expA ) {
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if ( ! sigA ) return a;
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normExpSig = softfloat_normSubnormalF16Sig( sigA );
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expA = normExpSig.exp;
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sigA = normExpSig.sig;
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}
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/*------------------------------------------------------------------------
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*------------------------------------------------------------------------*/
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rem = sigA | 0x0400;
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sigB |= 0x0400;
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expDiff = expA - expB;
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if ( expDiff < 1 ) {
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if ( expDiff < -1 ) return a;
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sigB <<= 3;
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if ( expDiff ) {
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rem <<= 2;
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q = 0;
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} else {
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rem <<= 3;
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q = (sigB <= rem);
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if ( q ) rem -= sigB;
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}
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} else {
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recip32 = softfloat_approxRecip32_1( (uint_fast32_t) sigB<<21 );
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/*--------------------------------------------------------------------
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| Changing the shift of `rem' here requires also changing the initial
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| subtraction from `expDiff'.
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*--------------------------------------------------------------------*/
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rem <<= 4;
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expDiff -= 31;
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/*--------------------------------------------------------------------
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| The scale of `sigB' affects how many bits are obtained during each
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| cycle of the loop. Currently this is 29 bits per loop iteration,
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| which is believed to be the maximum possible.
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*--------------------------------------------------------------------*/
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sigB <<= 3;
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for (;;) {
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q32 = (rem * (uint_fast64_t) recip32)>>16;
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if ( expDiff < 0 ) break;
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rem = -((uint_fast16_t) q32 * sigB);
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expDiff -= 29;
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}
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/*--------------------------------------------------------------------
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| (`expDiff' cannot be less than -30 here.)
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*--------------------------------------------------------------------*/
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q32 >>= ~expDiff & 31;
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q = q32;
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rem = (rem<<(expDiff + 30)) - q * sigB;
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}
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/*------------------------------------------------------------------------
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*------------------------------------------------------------------------*/
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do {
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altRem = rem;
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++q;
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rem -= sigB;
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} while ( ! (rem & 0x8000) );
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meanRem = rem + altRem;
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if ( (meanRem & 0x8000) || (! meanRem && (q & 1)) ) rem = altRem;
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signRem = signA;
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if ( 0x8000 <= rem ) {
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signRem = ! signRem;
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rem = -rem;
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}
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return softfloat_normRoundPackToF16( signRem, expB, rem );
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/*------------------------------------------------------------------------
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*------------------------------------------------------------------------*/
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propagateNaN:
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uiZ = softfloat_propagateNaNF16UI( uiA, uiB );
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goto uiZ;
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invalid:
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softfloat_raiseFlags( softfloat_flag_invalid );
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uiZ = defaultNaNF16UI;
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uiZ:
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uZ.ui = uiZ;
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return uZ.f;
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}
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