1 | |
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2 | /* @(#)s_floor.c 5.1 93/09/24 */ |
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3 | /* |
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4 | * ==================================================== |
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5 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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6 | * |
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7 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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8 | * Permission to use, copy, modify, and distribute this |
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9 | * software is freely granted, provided that this notice |
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10 | * is preserved. |
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11 | * ==================================================== |
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12 | */ |
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13 | |
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14 | /* |
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15 | * floor(x) |
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16 | * Return x rounded toward -inf to integral value |
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17 | * Method: |
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18 | * Bit twiddling. |
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19 | * Exception: |
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20 | * Inexact flag raised if x not equal to floor(x). |
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21 | */ |
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22 | |
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23 | #include <libm/fdlibm.h> |
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24 | |
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25 | #ifdef __STDC__ |
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26 | static const double one = 1.0,huge = 1.0e300; |
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27 | #else |
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28 | static double one = 1.0,huge = 1.0e300; |
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29 | #endif |
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30 | |
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31 | #ifdef __STDC__ |
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32 | double floor(double x) |
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33 | #else |
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34 | double floor(x) |
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35 | double x; |
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36 | #endif |
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37 | { |
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38 | int i0,i1,n0,j0; |
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39 | unsigned i,j; |
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40 | n0 = (*((int *)&one)>>29)^1; |
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41 | i0 = *(n0+(int*)&x); |
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42 | i1 = *(1-n0+(int*)&x); |
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43 | j0 = ((i0>>20)&0x7ff)-0x3ff; |
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44 | if(j0<20) { |
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45 | if(j0<0) { /* raise inexact if x != 0 */ |
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46 | if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */ |
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47 | if(i0>=0) {i0=i1=0;} |
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48 | else if(((i0&0x7fffffff)|i1)!=0) |
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49 | { i0=0xbff00000;i1=0;} |
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50 | } |
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51 | } else { |
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52 | i = (0x000fffff)>>j0; |
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53 | if(((i0&i)|i1)==0) return x; /* x is integral */ |
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54 | if(huge+x>0.0) { /* raise inexact flag */ |
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55 | if(i0<0) i0 += (0x00100000)>>j0; |
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56 | i0 &= (~i); i1=0; |
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57 | } |
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58 | } |
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59 | } else if (j0>51) { |
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60 | if(j0==0x400) return x+x; /* inf or NaN */ |
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61 | else return x; /* x is integral */ |
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62 | } else { |
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63 | i = ((unsigned)(0xffffffff))>>(j0-20); |
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64 | if((i1&i)==0) return x; /* x is integral */ |
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65 | if(huge+x>0.0) { /* raise inexact flag */ |
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66 | if(i0<0) { |
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67 | if(j0==20) i0+=1; |
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68 | else { |
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69 | j = i1+(1<<(52-j0)); |
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70 | if(j<(unsigned)i1) i0 +=1 ; /* got a carry */ |
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71 | i1=j; |
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72 | } |
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73 | } |
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74 | i1 &= (~i); |
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75 | } |
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76 | } |
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77 | *(n0+(int*)&x) = i0; |
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78 | *(1-n0+(int*)&x) = i1; |
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79 | return x; |
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80 | } |
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