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annotate src/libm/s_scalbn.c @ 3495:1b22878e04d0

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Adam Strzelecki to SDL D3D renderer shall try mapping YV12 and I420 (IYUV) to D3D texture formats via FOURCC. This will enable HW acceleration for those formats when driver is capable (most of them are). Note that SDL's IYUV maps I420 FOURCC on Woe.
author Sam Lantinga <slouken@libsdl.org>
date Fri, 27 Nov 2009 03:11:26 +0000
parents 9ac6f0782dd6
children
rev   line source
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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)