lib/builtins/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 /* This function should not call __divsi3! */
  24 COMPILER_RT_ABI su_int
  25 __udivsi3(su_int n, su_int d)
  26 {
  27     const unsigned n_uword_bits = sizeof(su_int) * CHAR_BIT;
  28     su_int q;
  29     su_int r;
  30     unsigned sr;
  31     /* special cases */
  32     if (d == 0)
  33         return 0; /* ?! */
  34     if (n == 0)
  35         return 0;
  36     sr = __builtin_clz(d) - __builtin_clz(n);
  37     /* 0 <= sr <= n_uword_bits - 1 or sr large */
  38     if (sr > n_uword_bits - 1)  /* d > r */
  39         return 0;
  40     if (sr == n_uword_bits - 1)  /* d == 1 */
  41         return n;
  42     ++sr;
  43     /* 1 <= sr <= n_uword_bits - 1 */
  44     /* Not a special case */
  45     q = n << (n_uword_bits - sr);
  46     r = n >> sr;
  47     su_int carry = 0;
  48     for (; sr > 0; --sr)
  49     {
  50         /* r:q = ((r:q)  << 1) | carry */
  51         r = (r << 1) | (q >> (n_uword_bits - 1));
  52         q = (q << 1) | carry;
  53         /* carry = 0;
  54          * if (r.all >= d.all)
  55          * {
  56          *      r.all -= d.all;
  57          *      carry = 1;
  58          * }
  59          */
  60         const si_int s = (si_int)(d - r - 1) >> (n_uword_bits - 1);
  61         carry = s & 1;
  62         r -= d & s;
  63     }
  64     q = (q << 1) | carry;
  65     return q;
  66 }