arch/sparc/lib/sdiv.S

   1 /* $Id: sdiv.S,v 1.6 1996/10/02 17:37:00 davem Exp $
   2  * sdiv.S:      This routine was taken from glibc-1.09 and is covered
   3  *              by the GNU Library General Public License Version 2.
   4  */
   5
   6
   7 /* This file is generated from divrem.m4; DO NOT EDIT! */
   8 /*
   9  * Division and remainder, from Appendix E of the Sparc Version 8
  10  * Architecture Manual, with fixes from Gordon Irlam.
  11  */
  12
  13 /*
  14  * Input: dividend and divisor in %o0 and %o1 respectively.
  15  *
  16  * m4 parameters:
  17  *  .div        name of function to generate
  18  *  div         div=div => %o0 / %o1; div=rem => %o0 % %o1
  19  *  true                true=true => signed; true=false => unsigned
  20  *
  21  * Algorithm parameters:
  22  *  N           how many bits per iteration we try to get (4)
  23  *  WORDSIZE    total number of bits (32)
  24  *
  25  * Derived constants:
  26  *  TOPBITS     number of bits in the top decade of a number
  27  *
  28  * Important variables:
  29  *  Q           the partial quotient under development (initially 0)
  30  *  R           the remainder so far, initially the dividend
  31  *  ITER        number of main division loop iterations required;
  32  *              equal to ceil(log2(quotient) / N).  Note that this
  33  *              is the log base (2^N) of the quotient.
  34  *  V           the current comparand, initially divisor*2^(ITER*N-1)
  35  *
  36  * Cost:
  37  *  Current estimate for non-large dividend is
  38  *      ceil(log2(quotient) / N) * (10 + 7N/2) + C
  39  *  A large dividend is one greater than 2^(31-TOPBITS) and takes a
  40  *  different path, as the upper bits of the quotient must be developed
  41  *  one bit at a time.
  42  */
  43
  44
  45         .globl .div
  46 .div:
  47         ! compute sign of result; if neither is negative, no problem
  48         orcc    %o1, %o0, %g0   ! either negative?
  49         bge     2f                      ! no, go do the divide
  50          xor    %o1, %o0, %g2   ! compute sign in any case
  51
  52         tst     %o1
  53         bge     1f
  54          tst    %o0
  55         ! %o1 is definitely negative; %o0 might also be negative
  56         bge     2f                      ! if %o0 not negative...
  57          sub    %g0, %o1, %o1   ! in any case, make %o1 nonneg
  58 1:      ! %o0 is negative, %o1 is nonnegative
  59         sub     %g0, %o0, %o0   ! make %o0 nonnegative
  60 2:
  61
  62         ! Ready to divide.  Compute size of quotient; scale comparand.
  63         orcc    %o1, %g0, %o5
  64         bne     1f
  65          mov    %o0, %o3
  66
  67                 ! Divide by zero trap.  If it returns, return 0 (about as
  68                 ! wrong as possible, but that is what SunOS does...).
  69                 ta      ST_DIV0
  70                 retl
  71                  clr    %o0
  72
  73 1:
  74         cmp     %o3, %o5                        ! if %o1 exceeds %o0, done
  75         blu     Lgot_result             ! (and algorithm fails otherwise)
  76          clr    %o2
  77
  78         sethi   %hi(1 << (32 - 4 - 1)), %g1
  79
  80         cmp     %o3, %g1
  81         blu     Lnot_really_big
  82          clr    %o4
  83
  84         ! Here the dividend is >= 2**(31-N) or so.  We must be careful here,
  85         ! as our usual N-at-a-shot divide step will cause overflow and havoc.
  86         ! The number of bits in the result here is N*ITER+SC, where SC <= N.
  87         ! Compute ITER in an unorthodox manner: know we need to shift V into
  88         ! the top decade: so do not even bother to compare to R.
  89         1:
  90                 cmp     %o5, %g1
  91                 bgeu    3f
  92                  mov    1, %g7
  93
  94                 sll     %o5, 4, %o5
  95
  96                 b       1b
  97                  add    %o4, 1, %o4
  98
  99         ! Now compute %g7.
 100         2:
 101                 addcc   %o5, %o5, %o5
 102                 bcc     Lnot_too_big
 103                  add    %g7, 1, %g7
 104
 105                 ! We get here if the %o1 overflowed while shifting.
 106                 ! This means that %o3 has the high-order bit set.
 107                 ! Restore %o5 and subtract from %o3.
 108                 sll     %g1, 4, %g1     ! high order bit
 109                 srl     %o5, 1, %o5             ! rest of %o5
 110                 add     %o5, %g1, %o5
 111
 112                 b       Ldo_single_div
 113                  sub    %g7, 1, %g7
 114
 115         Lnot_too_big:
 116         3:
 117                 cmp     %o5, %o3
 118                 blu     2b
 119                  nop
 120
 121                 be      Ldo_single_div
 122                  nop
 123         /* NB: these are commented out in the V8-Sparc manual as well */
 124         /* (I do not understand this) */
 125         ! %o5 > %o3: went too far: back up 1 step
 126         !       srl     %o5, 1, %o5
 127         !       dec     %g7
 128         ! do single-bit divide steps
 129         !
 130         ! We have to be careful here.  We know that %o3 >= %o5, so we can do the
 131         ! first divide step without thinking.  BUT, the others are conditional,
 132         ! and are only done if %o3 >= 0.  Because both %o3 and %o5 may have the high-
 133         ! order bit set in the first step, just falling into the regular
 134         ! division loop will mess up the first time around.
 135         ! So we unroll slightly...
 136         Ldo_single_div:
 137                 subcc   %g7, 1, %g7
 138                 bl      Lend_regular_divide
 139                  nop
 140
 141                 sub     %o3, %o5, %o3
 142                 mov     1, %o2
 143
 144                 b       Lend_single_divloop
 145                  nop
 146         Lsingle_divloop:
 147                 sll     %o2, 1, %o2
 148
 149                 bl      1f
 150                  srl    %o5, 1, %o5
 151                 ! %o3 >= 0
 152                 sub     %o3, %o5, %o3
 153
 154                 b       2f
 155                  add    %o2, 1, %o2
 156         1:      ! %o3 < 0
 157                 add     %o3, %o5, %o3
 158                 sub     %o2, 1, %o2
 159         2:
 160         Lend_single_divloop:
 161                 subcc   %g7, 1, %g7
 162                 bge     Lsingle_divloop
 163                  tst    %o3
 164
 165                 b,a     Lend_regular_divide
 166
 167 Lnot_really_big:
 168 1:
 169         sll     %o5, 4, %o5
 170         cmp     %o5, %o3
 171         bleu    1b
 172          addcc  %o4, 1, %o4
 173
 174         be      Lgot_result
 175          sub    %o4, 1, %o4
 176
 177         tst     %o3     ! set up for initial iteration
 178 Ldivloop:
 179         sll     %o2, 4, %o2
 180                 ! depth 1, accumulated bits 0
 181         bl      L.1.16
 182          srl    %o5,1,%o5
 183         ! remainder is positive
 184         subcc   %o3,%o5,%o3
 185                         ! depth 2, accumulated bits 1
 186         bl      L.2.17
 187          srl    %o5,1,%o5
 188         ! remainder is positive
 189         subcc   %o3,%o5,%o3
 190                         ! depth 3, accumulated bits 3
 191         bl      L.3.19
 192          srl    %o5,1,%o5
 193         ! remainder is positive
 194         subcc   %o3,%o5,%o3
 195                         ! depth 4, accumulated bits 7
 196         bl      L.4.23
 197          srl    %o5,1,%o5
 198         ! remainder is positive
 199         subcc   %o3,%o5,%o3
 200         b       9f
 201          add    %o2, (7*2+1), %o2
 202
 203 L.4.23:
 204         ! remainder is negative
 205         addcc   %o3,%o5,%o3
 206         b       9f
 207          add    %o2, (7*2-1), %o2
 208
 209 L.3.19:
 210         ! remainder is negative
 211         addcc   %o3,%o5,%o3
 212                         ! depth 4, accumulated bits 5
 213         bl      L.4.21
 214          srl    %o5,1,%o5
 215         ! remainder is positive
 216         subcc   %o3,%o5,%o3
 217         b       9f
 218          add    %o2, (5*2+1), %o2
 219
 220 L.4.21:
 221         ! remainder is negative
 222         addcc   %o3,%o5,%o3
 223         b       9f
 224          add    %o2, (5*2-1), %o2
 225
 226 L.2.17:
 227         ! remainder is negative
 228         addcc   %o3,%o5,%o3
 229                         ! depth 3, accumulated bits 1
 230         bl      L.3.17
 231          srl    %o5,1,%o5
 232         ! remainder is positive
 233         subcc   %o3,%o5,%o3
 234                         ! depth 4, accumulated bits 3
 235         bl      L.4.19
 236          srl    %o5,1,%o5
 237         ! remainder is positive
 238         subcc   %o3,%o5,%o3
 239         b       9f
 240          add    %o2, (3*2+1), %o2
 241
 242 L.4.19:
 243         ! remainder is negative
 244         addcc   %o3,%o5,%o3
 245         b       9f
 246          add    %o2, (3*2-1), %o2
 247
 248
 249 L.3.17:
 250         ! remainder is negative
 251         addcc   %o3,%o5,%o3
 252                         ! depth 4, accumulated bits 1
 253         bl      L.4.17
 254          srl    %o5,1,%o5
 255         ! remainder is positive
 256         subcc   %o3,%o5,%o3
 257         b       9f
 258          add    %o2, (1*2+1), %o2
 259
 260 L.4.17:
 261         ! remainder is negative
 262         addcc   %o3,%o5,%o3
 263         b       9f
 264          add    %o2, (1*2-1), %o2
 265
 266 L.1.16:
 267         ! remainder is negative
 268         addcc   %o3,%o5,%o3
 269                         ! depth 2, accumulated bits -1
 270         bl      L.2.15
 271          srl    %o5,1,%o5
 272         ! remainder is positive
 273         subcc   %o3,%o5,%o3
 274                         ! depth 3, accumulated bits -1
 275         bl      L.3.15
 276          srl    %o5,1,%o5
 277         ! remainder is positive
 278         subcc   %o3,%o5,%o3
 279                         ! depth 4, accumulated bits -1
 280         bl      L.4.15
 281          srl    %o5,1,%o5
 282         ! remainder is positive
 283         subcc   %o3,%o5,%o3
 284         b       9f
 285          add    %o2, (-1*2+1), %o2
 286
 287 L.4.15:
 288         ! remainder is negative
 289         addcc   %o3,%o5,%o3
 290         b       9f
 291          add    %o2, (-1*2-1), %o2
 292
 293 L.3.15:
 294         ! remainder is negative
 295         addcc   %o3,%o5,%o3
 296                         ! depth 4, accumulated bits -3
 297         bl      L.4.13
 298          srl    %o5,1,%o5
 299         ! remainder is positive
 300         subcc   %o3,%o5,%o3
 301         b       9f
 302          add    %o2, (-3*2+1), %o2
 303
 304 L.4.13:
 305         ! remainder is negative
 306         addcc   %o3,%o5,%o3
 307         b       9f
 308          add    %o2, (-3*2-1), %o2
 309
 310 L.2.15:
 311         ! remainder is negative
 312         addcc   %o3,%o5,%o3
 313                         ! depth 3, accumulated bits -3
 314         bl      L.3.13
 315          srl    %o5,1,%o5
 316         ! remainder is positive
 317         subcc   %o3,%o5,%o3
 318                         ! depth 4, accumulated bits -5
 319         bl      L.4.11
 320          srl    %o5,1,%o5
 321         ! remainder is positive
 322         subcc   %o3,%o5,%o3
 323         b       9f
 324          add    %o2, (-5*2+1), %o2
 325
 326 L.4.11:
 327         ! remainder is negative
 328         addcc   %o3,%o5,%o3
 329         b       9f
 330          add    %o2, (-5*2-1), %o2
 331
 332 L.3.13:
 333         ! remainder is negative
 334         addcc   %o3,%o5,%o3
 335                         ! depth 4, accumulated bits -7
 336         bl      L.4.9
 337          srl    %o5,1,%o5
 338         ! remainder is positive
 339         subcc   %o3,%o5,%o3
 340         b       9f
 341          add    %o2, (-7*2+1), %o2
 342
 343 L.4.9:
 344         ! remainder is negative
 345         addcc   %o3,%o5,%o3
 346         b       9f
 347          add    %o2, (-7*2-1), %o2
 348
 349         9:
 350 Lend_regular_divide:
 351         subcc   %o4, 1, %o4
 352         bge     Ldivloop
 353          tst    %o3
 354
 355         bl,a    Lgot_result
 356         ! non-restoring fixup here (one instruction only!)
 357         sub     %o2, 1, %o2
 358
 359 Lgot_result:
 360         ! check to see if answer should be < 0
 361         tst     %g2
 362         bl,a    1f
 363          sub %g0, %o2, %o2
 364 1:
 365         retl
 366          mov %o2, %o0
 367
 368         .globl  .div_patch
 369 .div_patch:
 370         sra     %o0, 0x1f, %o2
 371         wr      %o2, 0x0, %y
 372         nop
 373         nop
 374         nop
 375         sdivcc  %o0, %o1, %o0
 376         bvs,a   1f
 377          xnor   %o0, %g0, %o0
 378 1:      retl
 379          nop