lib/udivmodti4.c

   1 /* ===-- udivmodti4.c - Implement __udivmodti4 -----------------------------===
   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 __udivmodti4 for the compiler_rt library.
  11  *
  12  * ===----------------------------------------------------------------------===
  13  */
  14
  15 #include "int_lib.h"
  16
  17 #if __x86_64
  18
  19 /* Effects: if rem != 0, *rem = a % b
  20  * Returns: a / b
  21  */
  22
  23 /* Translated from Figure 3-40 of The PowerPC Compiler Writer's Guide */
  24
  25 tu_int
  26 __udivmodti4(tu_int a, tu_int b, tu_int* rem)
  27 {
  28     const unsigned n_udword_bits = sizeof(du_int) * CHAR_BIT;
  29     const unsigned n_utword_bits = sizeof(tu_int) * CHAR_BIT;
  30     utwords n;
  31     n.all = a;
  32     utwords d;
  33     d.all = b;
  34     utwords q;
  35     utwords r;
  36     unsigned sr;
  37     /* special cases, X is unknown, K != 0 */
  38     if (n.s.high == 0)
  39     {
  40         if (d.s.high == 0)
  41         {
  42             /* 0 X
  43              * ---
  44              * 0 X
  45              */
  46             if (rem)
  47                 *rem = n.s.low % d.s.low;
  48             return n.s.low / d.s.low;
  49         }
  50         /* 0 X
  51          * ---
  52          * K X
  53          */
  54         if (rem)
  55             *rem = n.s.low;
  56         return 0;
  57     }
  58     /* n.s.high != 0 */
  59     if (d.s.low == 0)
  60     {
  61         if (d.s.high == 0)
  62         {
  63             /* K X
  64              * ---
  65              * 0 0
  66              */
  67             if (rem)
  68                 *rem = n.s.high % d.s.low;
  69             return n.s.high / d.s.low;
  70         }
  71         /* d.s.high != 0 */
  72         if (n.s.low == 0)
  73         {
  74             /* K 0
  75              * ---
  76              * K 0
  77              */
  78             if (rem)
  79             {
  80                 r.s.high = n.s.high % d.s.high;
  81                 r.s.low = 0;
  82                 *rem = r.all;
  83             }
  84             return n.s.high / d.s.high;
  85         }
  86         /* K K
  87          * ---
  88          * K 0
  89          */
  90         if ((d.s.high & (d.s.high - 1)) == 0)     /* if d is a power of 2 */
  91         {
  92             if (rem)
  93             {
  94                 r.s.low = n.s.low;
  95                 r.s.high = n.s.high & (d.s.high - 1);
  96                 *rem = r.all;
  97             }
  98             return n.s.high >> __builtin_ctzll(d.s.high);
  99         }
 100         /* K K
 101          * ---
 102          * K 0
 103          */
 104         sr = __builtin_clzll(d.s.high) - __builtin_clzll(n.s.high);
 105         /* 0 <= sr <= n_udword_bits - 2 or sr large */
 106         if (sr > n_udword_bits - 2)
 107         {
 108            if (rem)
 109                 *rem = n.all;
 110             return 0;
 111         }
 112         ++sr;
 113         /* 1 <= sr <= n_udword_bits - 1 */
 114         /* q.all = n.all << (n_utword_bits - sr); */
 115         q.s.low = 0;
 116         q.s.high = n.s.low << (n_udword_bits - sr);
 117         /* r.all = n.all >> sr; */
 118         r.s.high = n.s.high >> sr;
 119         r.s.low = (n.s.high << (n_udword_bits - sr)) | (n.s.low >> sr);
 120     }
 121     else  /* d.s.low != 0 */
 122     {
 123         if (d.s.high == 0)
 124         {
 125             /* K X
 126              * ---
 127              * 0 K
 128              */
 129             if ((d.s.low & (d.s.low - 1)) == 0)     /* if d is a power of 2 */
 130             {
 131                 if (rem)
 132                     *rem = n.s.low & (d.s.low - 1);
 133                 if (d.s.low == 1)
 134                     return n.all;
 135                 sr = __builtin_ctzll(d.s.low);
 136                 q.s.high = n.s.high >> sr;
 137                 q.s.low = (n.s.high << (n_udword_bits - sr)) | (n.s.low >> sr);
 138                 return q.all;
 139             }
 140             /* K X
 141              * ---
 142              * 0 K
 143              */
 144             sr = 1 + n_udword_bits + __builtin_clzll(d.s.low)
 145                                    - __builtin_clzll(n.s.high);
 146             /* 2 <= sr <= n_utword_bits - 1
 147              * q.all = n.all << (n_utword_bits - sr);
 148              * r.all = n.all >> sr;
 149              * if (sr == n_udword_bits)
 150              * {
 151              *     q.s.low = 0;
 152              *     q.s.high = n.s.low;
 153              *     r.s.high = 0;
 154              *     r.s.low = n.s.high;
 155              * }
 156              * else if (sr < n_udword_bits)  // 2 <= sr <= n_udword_bits - 1
 157              * {
 158              *     q.s.low = 0;
 159              *     q.s.high = n.s.low << (n_udword_bits - sr);
 160              *     r.s.high = n.s.high >> sr;
 161              *     r.s.low = (n.s.high << (n_udword_bits - sr)) | (n.s.low >> sr);
 162              * }
 163              * else              // n_udword_bits + 1 <= sr <= n_utword_bits - 1
 164              * {
 165              *     q.s.low = n.s.low << (n_utword_bits - sr);
 166              *     q.s.high = (n.s.high << (n_utword_bits - sr)) |
 167              *              (n.s.low >> (sr - n_udword_bits));
 168              *     r.s.high = 0;
 169              *     r.s.low = n.s.high >> (sr - n_udword_bits);
 170              * }
 171              */
 172             q.s.low =  (n.s.low << (n_utword_bits - sr)) &
 173                      ((di_int)(int)(n_udword_bits - sr) >> (n_udword_bits-1));
 174             q.s.high = ((n.s.low << ( n_udword_bits - sr))                        &
 175                      ((di_int)(int)(sr - n_udword_bits - 1) >> (n_udword_bits-1))) |
 176                      (((n.s.high << (n_utword_bits - sr))                       |
 177                      (n.s.low >> (sr - n_udword_bits)))                         &
 178                      ((di_int)(int)(n_udword_bits - sr) >> (n_udword_bits-1)));
 179             r.s.high = (n.s.high >> sr) &
 180                      ((di_int)(int)(sr - n_udword_bits) >> (n_udword_bits-1));
 181             r.s.low =  ((n.s.high >> (sr - n_udword_bits))                        &
 182                      ((di_int)(int)(n_udword_bits - sr - 1) >> (n_udword_bits-1))) |
 183                      (((n.s.high << (n_udword_bits - sr))                       |
 184                      (n.s.low >> sr))                                           &
 185                      ((di_int)(int)(sr - n_udword_bits) >> (n_udword_bits-1)));
 186         }
 187         else
 188         {
 189             /* K X
 190              * ---
 191              * K K
 192              */
 193             sr = __builtin_clzll(d.s.high) - __builtin_clzll(n.s.high);
 194             /*0 <= sr <= n_udword_bits - 1 or sr large */
 195             if (sr > n_udword_bits - 1)
 196             {
 197                if (rem)
 198                     *rem = n.all;
 199                 return 0;
 200             }
 201             ++sr;
 202             /* 1 <= sr <= n_udword_bits */
 203             /* q.all = n.all << (n_utword_bits - sr); */
 204             q.s.low = 0;
 205             q.s.high = n.s.low << (n_udword_bits - sr);
 206             /* r.all = n.all >> sr;
 207              * if (sr < n_udword_bits)
 208              * {
 209              *     r.s.high = n.s.high >> sr;
 210              *     r.s.low = (n.s.high << (n_udword_bits - sr)) | (n.s.low >> sr);
 211              * }
 212              * else
 213              * {
 214              *     r.s.high = 0;
 215              *     r.s.low = n.s.high;
 216              * }
 217              */
 218             r.s.high = (n.s.high >> sr) &
 219                      ((di_int)(int)(sr - n_udword_bits) >> (n_udword_bits-1));
 220             r.s.low = (n.s.high << (n_udword_bits - sr)) |
 221                     ((n.s.low >> sr)                   &
 222                     ((di_int)(int)(sr - n_udword_bits) >> (n_udword_bits-1)));
 223         }
 224     }
 225     /* Not a special case
 226      * q and r are initialized with:
 227      * q.all = n.all << (n_utword_bits - sr);
 228      * r.all = n.all >> sr;
 229      * 1 <= sr <= n_utword_bits - 1
 230      */
 231     su_int carry = 0;
 232     for (; sr > 0; --sr)
 233     {
 234         /* r:q = ((r:q)  << 1) | carry */
 235         r.s.high = (r.s.high << 1) | (r.s.low  >> (n_udword_bits - 1));
 236         r.s.low  = (r.s.low  << 1) | (q.s.high >> (n_udword_bits - 1));
 237         q.s.high = (q.s.high << 1) | (q.s.low  >> (n_udword_bits - 1));
 238         q.s.low  = (q.s.low  << 1) | carry;
 239         /* carry = 0;
 240          * if (r.all >= d.all)
 241          * {
 242          *     r.all -= d.all;
 243          *      carry = 1;
 244          * }
 245          */
 246         const ti_int s = (ti_int)(d.all - r.all - 1) >> (n_utword_bits - 1);
 247         carry = s & 1;
 248         r.all -= d.all & s;
 249     }
 250     q.all = (q.all << 1) | carry;
 251     if (rem)
 252         *rem = r.all;
 253     return q.all;
 254 }
 255
 256 #endif /* __x86_64 */