137 lines
5.2 KiB
C
137 lines
5.2 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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extern const uint16_t softfloat_approxRecipSqrt_1k0s[];
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extern const uint16_t softfloat_approxRecipSqrt_1k1s[];
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float16_t f16_sqrt( float16_t a )
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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, uiZ;
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struct exp8_sig16 normExpSig;
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int_fast8_t expZ;
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int index;
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uint_fast16_t r0;
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uint_fast32_t ESqrR0;
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uint16_t sigma0;
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uint_fast16_t recipSqrt16, sigZ, shiftedSigZ;
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uint16_t negRem;
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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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/*------------------------------------------------------------------------
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*------------------------------------------------------------------------*/
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if ( expA == 0x1F ) {
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if ( sigA ) {
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uiZ = softfloat_propagateNaNF16UI( uiA, 0 );
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goto uiZ;
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}
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if ( ! signA ) return a;
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goto invalid;
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}
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/*------------------------------------------------------------------------
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*------------------------------------------------------------------------*/
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if ( signA ) {
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if ( ! (expA | sigA) ) return a;
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goto invalid;
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}
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/*------------------------------------------------------------------------
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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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expZ = ((expA - 0xF)>>1) + 0xE;
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expA &= 1;
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sigA |= 0x0400;
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index = (sigA>>6 & 0xE) + expA;
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r0 = softfloat_approxRecipSqrt_1k0s[index]
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- (((uint_fast32_t) softfloat_approxRecipSqrt_1k1s[index]
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* (sigA & 0x7F))
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>>11);
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ESqrR0 = ((uint_fast32_t) r0 * r0)>>1;
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if ( expA ) ESqrR0 >>= 1;
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sigma0 = ~(uint_fast16_t) ((ESqrR0 * sigA)>>16);
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recipSqrt16 = r0 + (((uint_fast32_t) r0 * sigma0)>>25);
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if ( ! (recipSqrt16 & 0x8000) ) recipSqrt16 = 0x8000;
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sigZ = ((uint_fast32_t) (sigA<<5) * recipSqrt16)>>16;
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if ( expA ) sigZ >>= 1;
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/*------------------------------------------------------------------------
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*------------------------------------------------------------------------*/
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++sigZ;
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if ( ! (sigZ & 7) ) {
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shiftedSigZ = sigZ>>1;
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negRem = shiftedSigZ * shiftedSigZ;
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sigZ &= ~1;
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if ( negRem & 0x8000 ) {
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sigZ |= 1;
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} else {
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if ( negRem ) --sigZ;
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}
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}
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return softfloat_roundPackToF16( 0, expZ, sigZ );
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/*------------------------------------------------------------------------
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*------------------------------------------------------------------------*/
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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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