How does one do integer (signed or unsigned) division on ARM?

Question

I\'m working on Cortex-A8 and Cortex-A9 in particular. I know that some architectures don\'t come with integer division, but what is the best way to do it other than convert

Answer 1

I wrote my own routine to perform an unsigned division as I could not find an unsigned version on the web. I needed to divide a 64 bit value with a 32 bit value to get a 32 bit result.

The inner loop is not as efficient as the signed solution provided above, but this does support unsigned arithmetic. This routine performs a 32 bit division if the high part of the numerator (hi) is smaller than the denominator (den), otherwise a full 64 bit division is performed (hi:lo/den). The result is in lo.

  cmp     hi, den                   // if hi < den do 32 bits, else 64 bits
  bpl     do64bits
  REPT    32
    adds    lo, lo, lo              // shift numerator through carry
    adcs    hi, hi, hi
    subscc  work, hi, den           // if carry not set, compare        
    subcs   hi, hi, den             // if carry set, subtract
    addcs   lo, lo, #1              // if carry set, and 1 to quotient
  ENDR

  mov     r0, lo                    // move result into R0
  mov     pc, lr                    // return

do64bits:
  mov     top, #0
  REPT    64
    adds    lo, lo, lo              // shift numerator through carry
    adcs    hi, hi, hi
    adcs    top, top, top
    subscc  work, top, den          // if carry not set, compare        
    subcs   top, top, den           // if carry set, subtract
    addcs   lo, lo, #1              // if carry set, and 1 to quotient
  ENDR
  mov     r0, lo                    // move result into R0
  mov     pc, lr                    // return

Extra checking for boundary conditions and power of 2 can be added. Full details can be found at http://www.idwiz.co.za/Tips%20and%20Tricks/Divide.htm