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source:
trunk/third/gmp/mpz/cfdiv_q_2exp.c
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Revision 22254, 2.8 KB checked in by ghudson, 19 years ago (diff) |
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1 | /* mpz_cdiv_q_2exp, mpz_fdiv_q_2exp -- quotient from mpz divided by 2^n. |

2 | |

3 | Copyright 1991, 1993, 1994, 1996, 1998, 1999, 2001, 2002, 2004 Free Software |

4 | Foundation, Inc. |

5 | |

6 | This file is part of the GNU MP Library. |

7 | |

8 | The GNU MP Library is free software; you can redistribute it and/or modify |

9 | it under the terms of the GNU Lesser General Public License as published by |

10 | the Free Software Foundation; either version 2.1 of the License, or (at your |

11 | option) any later version. |

12 | |

13 | The GNU MP Library is distributed in the hope that it will be useful, but |

14 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |

15 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |

16 | License for more details. |

17 | |

18 | You should have received a copy of the GNU Lesser General Public License |

19 | along with the GNU MP Library; see the file COPYING.LIB. If not, write to |

20 | the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |

21 | MA 02111-1307, USA. */ |

22 | |

23 | #include "gmp.h" |

24 | #include "gmp-impl.h" |

25 | |

26 | |

27 | /* dir==1 for ceil, dir==-1 for floor */ |

28 | |

29 | static void __gmpz_cfdiv_q_2exp _PROTO ((REGPARM_3_1 (mpz_ptr w, mpz_srcptr u, unsigned long cnt, int dir))) REGPARM_ATTR (1); |

30 | #define cfdiv_q_2exp(w,u,cnt,dir) __gmpz_cfdiv_q_2exp (REGPARM_3_1 (w,u,cnt,dir)) |

31 | |

32 | REGPARM_ATTR (1) static void |

33 | cfdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long cnt, int dir) |

34 | { |

35 | mp_size_t wsize, usize, abs_usize, limb_cnt, i; |

36 | mp_srcptr up; |

37 | mp_ptr wp; |

38 | mp_limb_t round, rmask; |

39 | |

40 | usize = SIZ (u); |

41 | abs_usize = ABS (usize); |

42 | limb_cnt = cnt / GMP_NUMB_BITS; |

43 | wsize = abs_usize - limb_cnt; |

44 | if (wsize <= 0) |

45 | { |

46 | /* u < 2**cnt, so result 1, 0 or -1 according to rounding */ |

47 | PTR(w)[0] = 1; |

48 | SIZ(w) = (usize == 0 || (usize ^ dir) < 0 ? 0 : dir); |

49 | return; |

50 | } |

51 | |

52 | /* +1 limb to allow for mpn_add_1 below */ |

53 | MPZ_REALLOC (w, wsize+1); |

54 | |

55 | /* Check for rounding if direction matches u sign. |

56 | Set round if we're skipping non-zero limbs. */ |

57 | up = PTR(u); |

58 | round = 0; |

59 | rmask = ((usize ^ dir) >= 0 ? MP_LIMB_T_MAX : 0); |

60 | if (rmask != 0) |

61 | for (i = 0; i < limb_cnt && round == 0; i++) |

62 | round = up[i]; |

63 | |

64 | wp = PTR(w); |

65 | cnt %= GMP_NUMB_BITS; |

66 | if (cnt != 0) |

67 | { |

68 | round |= rmask & mpn_rshift (wp, up + limb_cnt, wsize, cnt); |

69 | wsize -= (wp[wsize - 1] == 0); |

70 | } |

71 | else |

72 | MPN_COPY_INCR (wp, up + limb_cnt, wsize); |

73 | |

74 | if (round != 0) |

75 | { |

76 | if (wsize != 0) |

77 | { |

78 | mp_limb_t cy; |

79 | cy = mpn_add_1 (wp, wp, wsize, CNST_LIMB(1)); |

80 | wp[wsize] = cy; |

81 | wsize += cy; |

82 | } |

83 | else |

84 | { |

85 | /* We shifted something to zero. */ |

86 | wp[0] = 1; |

87 | wsize = 1; |

88 | } |

89 | } |

90 | SIZ(w) = (usize >= 0 ? wsize : -wsize); |

91 | } |

92 | |

93 | |

94 | void |

95 | mpz_cdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long cnt) |

96 | { |

97 | cfdiv_q_2exp (w, u, cnt, 1); |

98 | } |

99 | |

100 | void |

101 | mpz_fdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long cnt) |

102 | { |

103 | cfdiv_q_2exp (w, u, cnt, -1); |

104 | } |

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