source/s_approxRecipSqrt32_1.c

/*============================================================================

This C source file is part of the SoftFloat IEEE Floating-Point Arithmetic
Package, Release 3, by John R. Hauser.

Copyright 2011, 2012, 2013, 2014 The Regents of the University of California
(Regents).  All Rights Reserved.  Redistribution and use in source and binary
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this list of conditions, and the following two paragraphs of disclaimer.
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the name of the Regents nor the names of its contributors may be used to
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=============================================================================*/

#include <stdint.h>
#include "platform.h"
#include "primitives.h"

#ifndef softfloat_approxRecipSqrt32_1

uint32_t softfloat_approxRecipSqrt32_1( unsigned int oddExpA, uint32_t a )
{
    int index;
    uint16_t eps;
    static const uint16_t k0s[] = {
        0xB4C9, 0xFFAB, 0xAA7D, 0xF11C, 0xA1C5, 0xE4C7, 0x9A43, 0xDA29,
        0x93B5, 0xD0E5, 0x8DED, 0xC8B7, 0x88C6, 0xC16D, 0x8424, 0xBAE1
    };
    static const uint16_t k1s[] = {
        0xA5A5, 0xEA42, 0x8C21, 0xC62D, 0x788F, 0xAA7F, 0x6928, 0x94B6,
        0x5CC7, 0x8335, 0x52A6, 0x74E2, 0x4A3E, 0x68FE, 0x432B, 0x5EFD
    };
    uint16_t r0;
    uint_fast32_t ESqrR0;
    uint32_t delta0;
    uint_fast32_t r;
    uint32_t sqrDelta0;

    index = (a>>27 & 0xE) + oddExpA;
    eps = (uint16_t) (a>>12);
    r0 = k0s[index] - ((k1s[index] * (uint_fast32_t) eps)>>20);
    ESqrR0 = (uint_fast32_t) r0 * r0;
    if ( ! oddExpA ) ESqrR0 <<= 1;
    delta0 = ~(uint_fast32_t) (((uint32_t) ESqrR0 * (uint_fast64_t) a)>>23);
    r = ((uint_fast32_t) r0<<16) + ((r0 * (uint_fast64_t) delta0)>>25);
    sqrDelta0 = ((uint_fast64_t) delta0 * delta0)>>32;
    r += ((uint32_t) ((r>>1) + (r>>3) - ((uint_fast32_t) r0<<14))
              * (uint_fast64_t) sqrDelta0)
             >>48;
    if ( ! (r & 0x80000000) ) r = 0x80000000;
    return r;

}

#endif