root/arch/powerpc/lib/div64.S

   1 /* SPDX-License-Identifier: GPL-2.0-or-later */
   2 /*
   3  * Divide a 64-bit unsigned number by a 32-bit unsigned number.
   4  * This routine assumes that the top 32 bits of the dividend are
   5  * non-zero to start with.
   6  * On entry, r3 points to the dividend, which get overwritten with
   7  * the 64-bit quotient, and r4 contains the divisor.
   8  * On exit, r3 contains the remainder.
   9  *
  10  * Copyright (C) 2002 Paul Mackerras, IBM Corp.
  11  */
  12 #include <asm/ppc_asm.h>
  13 #include <asm/processor.h>
  14 
  15 _GLOBAL(__div64_32)
  16         lwz     r5,0(r3)        # get the dividend into r5/r6
  17         lwz     r6,4(r3)
  18         cmplw   r5,r4
  19         li      r7,0
  20         li      r8,0
  21         blt     1f
  22         divwu   r7,r5,r4        # if dividend.hi >= divisor,
  23         mullw   r0,r7,r4        # quotient.hi = dividend.hi / divisor
  24         subf.   r5,r0,r5        # dividend.hi %= divisor
  25         beq     3f
  26 1:      mr      r11,r5          # here dividend.hi != 0
  27         andis.  r0,r5,0xc000
  28         bne     2f
  29         cntlzw  r0,r5           # we are shifting the dividend right
  30         li      r10,-1          # to make it < 2^32, and shifting
  31         srw     r10,r10,r0      # the divisor right the same amount,
  32         addc    r9,r4,r10       # rounding up (so the estimate cannot
  33         andc    r11,r6,r10      # ever be too large, only too small)
  34         andc    r9,r9,r10
  35         addze   r9,r9
  36         or      r11,r5,r11
  37         rotlw   r9,r9,r0
  38         rotlw   r11,r11,r0
  39         divwu   r11,r11,r9      # then we divide the shifted quantities
  40 2:      mullw   r10,r11,r4      # to get an estimate of the quotient,
  41         mulhwu  r9,r11,r4       # multiply the estimate by the divisor,
  42         subfc   r6,r10,r6       # take the product from the divisor,
  43         add     r8,r8,r11       # and add the estimate to the accumulated
  44         subfe.  r5,r9,r5        # quotient
  45         bne     1b
  46 3:      cmplw   r6,r4
  47         blt     4f
  48         divwu   r0,r6,r4        # perform the remaining 32-bit division
  49         mullw   r10,r0,r4       # and get the remainder
  50         add     r8,r8,r0
  51         subf    r6,r10,r6
  52 4:      stw     r7,0(r3)        # return the quotient in *r3
  53         stw     r8,4(r3)
  54         mr      r3,r6           # return the remainder in r3
  55         blr