lib/udivmodti4.c

//===-- udivmodti4.c - Implement __udivmodti4 -----------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements __udivmodti4 for the compiler_rt library.
//
//===----------------------------------------------------------------------===//

#if __x86_64

#include "int_lib.h"

// Effects: if rem != 0, *rem = a % b
// Returns: a / b

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

tu_int
__udivmodti4(tu_int a, tu_int b, tu_int* rem)
{
    const unsigned n_udword_bits = sizeof(du_int) * CHAR_BIT;
    const unsigned n_utword_bits = sizeof(tu_int) * CHAR_BIT;
    utwords n;
    n.all = a;
    utwords d;
    d.all = b;
    utwords q;
    utwords r;
    unsigned sr;
    // special cases, X is unknown, K != 0
    if (n.high == 0)
    {
        if (d.high == 0)
        {
            // 0 X
            // ---
            // 0 X
            if (rem)
                *rem = n.low % d.low;
            return n.low / d.low;
        }
        // 0 X
        // ---
        // K X
        if (rem)
            *rem = n.low;
        return 0;
    }
    // n.high != 0
    if (d.low == 0)
    {
        if (d.high == 0)
        {
            // K X
            // ---
            // 0 0
            if (rem)
                *rem = n.high % d.low;
            return n.high / d.low;
        }
        // d.high != 0
        if (n.low == 0)
        {
            // K 0
            // ---
            // K 0
            if (rem)
            {
                r.high = n.high % d.high;
                r.low = 0;
                *rem = r.all;
            }
            return n.high / d.high;
        }
        // K K
        // ---
        // K 0
        if ((d.high & (d.high - 1)) == 0)     // if d is a power of 2
        {
            if (rem)
            {
                r.low = n.low;
                r.high = n.high & (d.high - 1);
                *rem = r.all;
            }
            return n.high >> __builtin_ctzll(d.high);
        }
        // K K
        // ---
        // K 0
        sr = __builtin_clzll(d.high) - __builtin_clzll(n.high);
        // 0 <= sr <= n_udword_bits - 2 or sr large
        if (sr > n_udword_bits - 2)
        {
           if (rem)
                *rem = n.all;
            return 0;
        }
        ++sr;
        // 1 <= sr <= n_udword_bits - 1
        // q.all = n.all << (n_utword_bits - sr);
        q.low = 0;
        q.high = n.low << (n_udword_bits - sr);
        // r.all = n.all >> sr;
        r.high = n.high >> sr;
        r.low = (n.high << (n_udword_bits - sr)) | (n.low >> sr);
    }
    else  // d.low != 0
    {
        if (d.high == 0)
        {
            // K X
            // ---
            // 0 K
            if ((d.low & (d.low - 1)) == 0)     // if d is a power of 2
            {
                if (rem)
                    *rem = n.low & (d.low - 1);
                if (d.low == 1)
                    return n.all;
                unsigned sr = __builtin_ctzll(d.low);
                q.high = n.high >> sr;
                q.low = (n.high << (n_udword_bits - sr)) | (n.low >> sr);
                return q.all;
            }
            // K X
            // ---
            // 0 K
            sr = 1 + n_udword_bits + __builtin_clzll(d.low)
                                   - __builtin_clzll(n.high);
            // 2 <= sr <= n_utword_bits - 1
            // q.all = n.all << (n_utword_bits - sr);
            // r.all = n.all >> sr;
            // if (sr == n_udword_bits)
            // {
            //     q.low = 0;
            //     q.high = n.low;
            //     r.high = 0;
            //     r.low = n.high;
            // }
            // else if (sr < n_udword_bits)  // 2 <= sr <= n_udword_bits - 1
            // {
            //     q.low = 0;
            //     q.high = n.low << (n_udword_bits - sr);
            //     r.high = n.high >> sr;
            //     r.low = (n.high << (n_udword_bits - sr)) | (n.low >> sr);
            // }
            // else              // n_udword_bits + 1 <= sr <= n_utword_bits - 1
            // {
            //     q.low = n.low << (n_utword_bits - sr);
            //     q.high = (n.high << (n_utword_bits - sr)) |
            //              (n.low >> (sr - n_udword_bits));
            //     r.high = 0;
            //     r.low = n.high >> (sr - n_udword_bits);
            // }
            q.low =  (n.low << (n_utword_bits - sr)) &
                     ((di_int)(int)(n_udword_bits - sr) >> (n_udword_bits-1));
            q.high = ((n.low << ( n_udword_bits - sr))                        &
                     ((di_int)(int)(sr - n_udword_bits - 1) >> (n_udword_bits-1))) |
                     (((n.high << (n_utword_bits - sr))                       |
                     (n.low >> (sr - n_udword_bits)))                         &
                     ((di_int)(int)(n_udword_bits - sr) >> (n_udword_bits-1)));
            r.high = (n.high >> sr) &
                     ((di_int)(int)(sr - n_udword_bits) >> (n_udword_bits-1));
            r.low =  ((n.high >> (sr - n_udword_bits))                        &
                     ((di_int)(int)(n_udword_bits - sr - 1) >> (n_udword_bits-1))) |
                     (((n.high << (n_udword_bits - sr))                       |
                     (n.low >> sr))                                           &
                     ((di_int)(int)(sr - n_udword_bits) >> (n_udword_bits-1)));
        }
        else
        {
            // K X
            // ---
            // K K
            sr = __builtin_clzll(d.high) - __builtin_clzll(n.high);
            // 0 <= sr <= n_udword_bits - 1 or sr large
            if (sr > n_udword_bits - 1)
            {
               if (rem)
                    *rem = n.all;
                return 0;
            }
            ++sr;
            // 1 <= sr <= n_udword_bits
            // q.all = n.all << (n_utword_bits - sr);
            q.low = 0;
            q.high = n.low << (n_udword_bits - sr);
            // r.all = n.all >> sr;
            // if (sr < n_udword_bits)
            // {
            //     r.high = n.high >> sr;
            //     r.low = (n.high << (n_udword_bits - sr)) | (n.low >> sr);
            // }
            // else
            // {
            //     r.high = 0;
            //     r.low = n.high;
            // }
            r.high = (n.high >> sr) &
                     ((di_int)(int)(sr - n_udword_bits) >> (n_udword_bits-1));
            r.low = (n.high << (n_udword_bits - sr)) |
                    ((n.low >> sr)                   &
                    ((di_int)(int)(sr - n_udword_bits) >> (n_udword_bits-1)));
        }
    }
    // Not a special case
    // q and r are initialized with:
    // q.all = n.all << (n_utword_bits - sr);
    // r.all = n.all >> sr;
    // 1 <= sr <= n_utword_bits - 1
    su_int carry = 0;
    for (; sr > 0; --sr)
    {
        // r:q = ((r:q)  << 1) | carry
        r.high = (r.high << 1) | (r.low  >> (n_udword_bits - 1));
        r.low  = (r.low  << 1) | (q.high >> (n_udword_bits - 1));
        q.high = (q.high << 1) | (q.low  >> (n_udword_bits - 1));
        q.low  = (q.low  << 1) | carry;
        // carry = 0;
        // if (r.all >= d.all)
        // {
        //      r.all -= d.all;
        //      carry = 1;
        // }
        const ti_int s = (ti_int)(d.all - r.all - 1) >> (n_utword_bits - 1);
        carry = s & 1;
        r.all -= d.all & s;
    }
    q.all = (q.all << 1) | carry;
    if (rem)
        *rem = r.all;
    return q.all;
}

#endif