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annotate src/libm/s_scalbn.c @ 4833:34fb492cefe3

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Shaped windows for Cocoa build and testshape runs, but the actual shaping doesn't work. Something, however, is definitely happening, because we get the backgrounds drawn in two different colors.
author egottlieb
date Thu, 05 Aug 2010 01:03:24 -0400
parents 9ac6f0782dd6
children
rev   line source
2756
a98604b691c8 Expanded the libm support and put it into a separate directory.
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1 /* @(#)s_scalbn.c 5.1 93/09/24 */
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2 /*
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3 * ====================================================
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4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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5 *
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6 * Developed at SunPro, a Sun Microsystems, Inc. business.
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7 * Permission to use, copy, modify, and distribute this
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8 * software is freely granted, provided that this notice
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9 * is preserved.
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10 * ====================================================
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11 */
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12
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13 #if defined(LIBM_SCCS) && !defined(lint)
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14 static const char rcsid[] =
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15 "$NetBSD: s_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc Exp $";
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16 #endif
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17
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18 /*
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19 * scalbn (double x, int n)
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20 * scalbn(x,n) returns x* 2**n computed by exponent
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21 * manipulation rather than by actually performing an
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22 * exponentiation or a multiplication.
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23 */
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24
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25 #include "math.h"
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26 #include "math_private.h"
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27
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28 libm_hidden_proto(copysign)
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29 #ifdef __STDC__
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30 static const double
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31 #else
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32 static double
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33 #endif
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34 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
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35 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
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36 huge_val = 1.0e+300, tiny = 1.0e-300;
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37
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38 libm_hidden_proto(scalbn)
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39 #ifdef __STDC__
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40 double scalbn(double x, int n)
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41 #else
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42 double scalbn(x, n)
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43 double x;
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44 int n;
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45 #endif
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46 {
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47 int32_t k, hx, lx;
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48 EXTRACT_WORDS(hx, lx, x);
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49 k = (hx & 0x7ff00000) >> 20; /* extract exponent */
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50 if (k == 0) { /* 0 or subnormal x */
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51 if ((lx | (hx & 0x7fffffff)) == 0)
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52 return x; /* +-0 */
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53 x *= two54;
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54 GET_HIGH_WORD(hx, x);
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55 k = ((hx & 0x7ff00000) >> 20) - 54;
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56 if (n < -50000)
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57 return tiny * x; /*underflow */
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58 }
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59 if (k == 0x7ff)
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60 return x + x; /* NaN or Inf */
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61 k = k + n;
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62 if (k > 0x7fe)
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63 return huge_val * copysign(huge_val, x); /* overflow */
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64 if (k > 0) { /* normal result */
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65 SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
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66 return x;
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67 }
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68 if (k <= -54) {
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69 if (n > 50000) /* in case integer overflow in n+k */
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70 return huge_val * copysign(huge_val, x); /*overflow */
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71 else
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72 return tiny * copysign(tiny, x); /*underflow */
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73 }
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74 k += 54; /* subnormal result */
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75 SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
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76 return x * twom54;
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77 }
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78
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79 libm_hidden_def(scalbn)