arch/ppc/boot/lib/div64.S

   1 /*
   2  * Divide a 64-bit unsigned number by a 32-bit unsigned number.
   3  * This routine assumes that the top 32 bits of the dividend are
   4  * non-zero to start with.
   5  * On entry, r3 points to the dividend, which get overwritten with
   6  * the 64-bit quotient, and r4 contains the divisor.
   7  * On exit, r3 contains the remainder.
   8  *
   9  * Copyright (C) 2002 Paul Mackerras, IBM Corp.
  10  *
  11  * This program is free software; you can redistribute it and/or
  12  * modify it under the terms of the GNU General Public License
  13  * as published by the Free Software Foundation; either version
  14  * 2 of the License, or (at your option) any later version.
  15  */
  16 #include <asm/ppc_asm.h>
  17 #include <asm/processor.h>
  18
  19 _GLOBAL(__div64_32)
  20         lwz     r5,0(r3)        # get the dividend into r5/r6
  21         lwz     r6,4(r3)
  22         cmplw   r5,r4
  23         li      r7,0
  24         li      r8,0
  25         blt     1f
  26         divwu   r7,r5,r4        # if dividend.hi >= divisor,
  27         mullw   r0,r7,r4        # quotient.hi = dividend.hi / divisor
  28         subf.   r5,r0,r5        # dividend.hi %= divisor
  29         beq     3f
  30 1:      mr      r11,r5          # here dividend.hi != 0
  31         andis.  r0,r5,0xc000
  32         bne     2f
  33         cntlzw  r0,r5           # we are shifting the dividend right
  34         li      r10,-1          # to make it < 2^32, and shifting
  35         srw     r10,r10,r0      # the divisor right the same amount,
  36         add     r9,r4,r10       # rounding up (so the estimate cannot
  37         andc    r11,r6,r10      # ever be too large, only too small)
  38         andc    r9,r9,r10
  39         or      r11,r5,r11
  40         rotlw   r9,r9,r0
  41         rotlw   r11,r11,r0
  42         divwu   r11,r11,r9      # then we divide the shifted quantities
  43 2:      mullw   r10,r11,r4      # to get an estimate of the quotient,
  44         mulhwu  r9,r11,r4       # multiply the estimate by the divisor,
  45         subfc   r6,r10,r6       # take the product from the divisor,
  46         add     r8,r8,r11       # and add the estimate to the accumulated
  47         subfe.  r5,r9,r5        # quotient
  48         bne     1b
  49 3:      cmplw   r6,r4
  50         blt     4f
  51         divwu   r0,r6,r4        # perform the remaining 32-bit division
  52         mullw   r10,r0,r4       # and get the remainder
  53         add     r8,r8,r0
  54         subf    r6,r10,r6
  55 4:      stw     r7,0(r3)        # return the quotient in *r3
  56         stw     r8,4(r3)
  57         mr      r3,r6           # return the remainder in r3
  58         blr