52 lines
1.6 KiB
C
Executable File
52 lines
1.6 KiB
C
Executable File
/* sqrtf.c: Computes square root of a 32-bit float as outlined in [1]
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Copyright (C) 2001, 2002 Jesus Calvino-Fraga, jesusc@ieee.org
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
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/* [1] William James Cody and W. M. Waite. _Software manual for the
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elementary functions_, Englewood Cliffs, N.J.:Prentice-Hall, 1980. */
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/* Version 1.0 - Initial release */
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#include "math.h"
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#include "errno.h"
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float sqrtf(const float x) _FLOAT_FUNC_REENTRANT
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{
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float f, y;
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int n;
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if (x==0.0) return x;
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else if (x==1.0) return 1.0;
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else if (x<0.0)
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{
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errno=EDOM;
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return 0.0;
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}
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f=frexpf(x, &n);
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y=0.41731+0.59016*f; /*Educated guess*/
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/*For a 24 bit mantisa (float), two iterations are sufficient*/
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y+=f/y;
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y=ldexpf(y, -2) + f/y; /*Faster version of 0.25 * y + f/y*/
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if (n&1)
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{
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y*=0.7071067812;
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++n;
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}
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return ldexpf(y, n/2);
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}
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