compiler-rt/lib/builtins/avr/udivmodhi4.S

   1 //===------------ udivmodhi4.S - uint16 div & mod -------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // As described at
  10 // https://gcc.gnu.org/wiki/avr-gcc#Exceptions_to_the_Calling_Convention, the
  11 // prototype is `struct {uint16, uint16}  __udivmodhi4(uint16, uint16)`.
  12 // The uint16 quotient is returned via R23:R22, and the uint16 remainder is
  13 // returned via R25:R24, while R21/R26/R27 are clobbered.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17         .text
  18         .align 2
  19
  20         .globl __udivmodhi4
  21         .type  __udivmodhi4, @function
  22
  23 __udivmodhi4:
  24         sub     r26, r26
  25         sub     r27, r27           ; Initialize the remainder to zero.
  26         ldi     r21, 17            ; Only loop 16 rounds for uint16.
  27
  28 __udivmodhi4_loop:
  29         adc     r24, r24
  30         adc     r25, r25
  31         dec     r21
  32         breq    __udivmodhi4_end
  33         adc     r26, r26
  34         adc     r27, r27
  35         cp      r26, r22
  36         cpc     r27, r23           ; Compare with the divisor.
  37         brcs    __udivmodhi4_loop
  38         sub     r26, r22
  39         sbc     r27, r23           ; Subtract the divisor.
  40         rjmp    __udivmodhi4_loop
  41
  42 __udivmodhi4_end:
  43         com     r24
  44         com     r25
  45         mov     r22, r24
  46         mov     r23, r25           ; The quotient is returned in R23:R22.
  47         mov     r24, r26
  48         mov     r25, r27           ; The remainder is returned in in R25:R24.
  49         ret