lib/udivsi3.c

//===-- udivsi3.c - Implement __udivsi3 -----------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements __udivsi3 for the compiler_rt library.
//
//===----------------------------------------------------------------------===//

#include "int_lib.h"

// Returns: a / b

// Translated from Figure 3-40 of The PowerPC Compiler Writer's Guide

su_int
__udivsi3(su_int n, su_int d)
{
    const unsigned n_uword_bits = sizeof(su_int) * CHAR_BIT;
    su_int q;
    su_int r;
    unsigned sr;
    // special cases
    if (d == 0)
        return 0; // ?!
    if (n == 0)
        return 0;
    sr = __builtin_clz(d) - __builtin_clz(n);
    // 0 <= sr <= n_uword_bits - 1 or sr large
    if (sr > n_uword_bits - 1)  // d > r
        return 0;
    if (sr == n_uword_bits - 1)  // d == 1
        return n;
    ++sr;
    // 1 <= sr <= n_uword_bits - 1
    // Not a special case
    q = n << (n_uword_bits - sr);
    r = n >> sr;
    su_int carry = 0;
    for (; sr > 0; --sr)
    {
        // r:q = ((r:q)  << 1) | carry
        r = (r << 1) | (q >> (n_uword_bits - 1));
        q = (q << 1) | carry;
        // carry = 0;
        // if (r.all >= d.all)
        // {
        //      r.all -= d.all;
        //      carry = 1;
        // }
        const si_int s = (si_int)(d - r - 1) >> (n_uword_bits - 1);
        carry = s & 1;
        r -= d & s;
    }
    q = (q << 1) | carry;
    return q;
}