49d1a4c562
also start prefering NtDll API. so far: * NtQueryInformationFile * NtClose adds a performance workaround for windows unicode conversion. but that should probably be removed before merging
76 lines
1.3 KiB
C
76 lines
1.3 KiB
C
/**
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* This file has no copyright assigned and is placed in the Public Domain.
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* This file is part of the mingw-w64 runtime package.
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* No warranty is given; refer to the file DISCLAIMER.PD within this package.
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*/
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#include <math.h>
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#include "cephes_mconf.h"
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static const float CBRT2 = 1.25992104989487316477;
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static const float CBRT4 = 1.58740105196819947475;
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float cbrtf (float x)
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{
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int e, rem, sign;
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float z;
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if (!isfinite (x) || x == 0.0F)
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return x;
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if (x > 0)
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sign = 1;
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else
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{
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sign = -1;
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x = -x;
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}
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z = x;
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/* extract power of 2, leaving
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* mantissa between 0.5 and 1
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*/
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x = frexpf(x, &e);
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/* Approximate cube root of number between .5 and 1,
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* peak relative error = 9.2e-6
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*/
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x = (((-0.13466110473359520655053 * x
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+ 0.54664601366395524503440 ) * x
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- 0.95438224771509446525043 ) * x
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+ 1.1399983354717293273738 ) * x
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+ 0.40238979564544752126924;
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/* exponent divided by 3 */
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if (e >= 0)
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{
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rem = e;
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e /= 3;
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rem -= 3*e;
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if (rem == 1)
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x *= CBRT2;
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else if (rem == 2)
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x *= CBRT4;
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}
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/* argument less than 1 */
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else
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{
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e = -e;
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rem = e;
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e /= 3;
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rem -= 3*e;
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if (rem == 1)
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x /= CBRT2;
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else if (rem == 2)
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x /= CBRT4;
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e = -e;
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}
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/* multiply by power of 2 */
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x = ldexpf(x, e);
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/* Newton iteration */
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x -= ( x - (z/(x*x)) ) * 0.333333333333;
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if (sign < 0)
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x = -x;
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return (x);
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}
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