lib/udivsi3.c

   1 /* ===-- udivsi3.c - Implement __udivsi3 -----------------------------------===
   2  *
   3  *                     The LLVM Compiler Infrastructure
   4  *
   5  * This file is dual licensed under the MIT and the University of Illinois Open
   6  * Source Licenses. See LICENSE.TXT for details.
   7  *
   8  * ===----------------------------------------------------------------------===
   9  *
  10  * This file implements __udivsi3 for the compiler_rt library.
  11  *
  12  * ===----------------------------------------------------------------------===
  13  */
  14
  15 #include "int_lib.h"
  16
  17 /* Returns: a / b */
  18
  19 /* Translated from Figure 3-40 of The PowerPC Compiler Writer's Guide */
  20
  21 ARM_EABI_FNALIAS(uidiv, udivsi3);
  22
  23 COMPILER_RT_ABI su_int
  24 __udivsi3(su_int n, su_int d)
  25 {
  26     const unsigned n_uword_bits = sizeof(su_int) * CHAR_BIT;
  27     su_int q;
  28     su_int r;
  29     unsigned sr;
  30     /* special cases */
  31     if (d == 0)
  32         return 0; /* ?! */
  33     if (n == 0)
  34         return 0;
  35     sr = __builtin_clz(d) - __builtin_clz(n);
  36     /* 0 <= sr <= n_uword_bits - 1 or sr large */
  37     if (sr > n_uword_bits - 1)  /* d > r */
  38         return 0;
  39     if (sr == n_uword_bits - 1)  /* d == 1 */
  40         return n;
  41     ++sr;
  42     /* 1 <= sr <= n_uword_bits - 1 */
  43     /* Not a special case */
  44     q = n << (n_uword_bits - sr);
  45     r = n >> sr;
  46     su_int carry = 0;
  47     for (; sr > 0; --sr)
  48     {
  49         /* r:q = ((r:q)  << 1) | carry */
  50         r = (r << 1) | (q >> (n_uword_bits - 1));
  51         q = (q << 1) | carry;
  52         /* carry = 0;
  53          * if (r.all >= d.all)
  54          * {
  55          *      r.all -= d.all;
  56          *      carry = 1;
  57          * }
  58          */
  59         const si_int s = (si_int)(d - r - 1) >> (n_uword_bits - 1);
  60         carry = s & 1;
  61         r -= d & s;
  62     }
  63     q = (q << 1) | carry;
  64     return q;
  65 }