udivsi3.c revision 229135 
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
21ARM_EABI_FNALIAS(uidiv, udivsi3);
22
23COMPILER_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}
66