int32.s

  .intel_syntax noprefix

_add:
  mov eax, edi
  add eax, esi
  jo plus_overflow
  jmp r8
plus_overflow:
  jmp r9

_null:
  cmp edi, 0
  jne null_is_not
  jmp r8
null_is_not:
  jmp r9

_times:
  mov eax, edi
  imul eax, esi
  jo times_overflow
  jmp r8
times_overflow:
  jmp r9

  ## toPower algorithm:
  ## 0 ** n = 0
  ## 1 ** n = 1
  ## x ** 0 = 1
  ## decompose the exponent n in powers of two
  ## for each factor k, x ** n = product( x ** k )
  ## so we can square x until we get the answer 
  ## example: 3 ** 5 = (3 ** 1) * (3 ** 4)
  ##                 = 3 * ((3 * 3) * (3 * 3))
  ##                 = 243
  .p2align  4
_toPower:
  mov eax, 0
  cmp edi, 0
  je toPower_success                ## shortcut if arg1 = 0
  mov eax, 1
  cmp edi, 1
  je toPower_success                ## shortcut if arg1 = 1
  cmp esi, 0
  je toPower_success                ## shortcut if arg2 = 0
  jl toPower_failed                 ## cannot do negative numbers
  push r8                           ## save return continuation
  push r9                           ## save event continuation
  mov eax, 1
  push rax                          ## calculation results
  lea r9, [rip + toPower_overflow]
  mov ecx, esi
toPower_loop:
  test ecx, 1
  jz toPower_next                   ## if exponent bit not set, don't update result
  pop rsi
  lea r8, [rip + toPower1]
  jmp _times                        ## note: assumes ecx is preserved
toPower1:
  push rax
toPower_next:
  shr ecx, 1
  jz toPower_done
  mov esi, edi
  lea r8, [rip + toPower2]
  jmp _times                        ## note: assumes ecx is preserved
toPower2:
  mov edi, eax                      ## take square of edi
  jmp toPower_loop
toPower_done:
  pop rax
  pop r9
  pop r8
toPower_success:
  jmp r8 
toPower_overflow:
  pop rax
  pop r9
  pop r8
toPower_failed:
  jmp r9

  .globl  _main                   ## -- Begin function main
  .p2align  4
_main:                                  ## @main
  mov edi, 3
  mov esi, 56
  lea r8, [rip + next]
  lea r9, [rip + zero]
  jmp _toPower
zero:
  mov eax, -1
next:
  ret
                                        ## -- End function
  .data
  .globl  _int32

_int32:
  .long 0
outofmemory_message:
  .asciz "ERROR: Out of memory"

lldb trace

(lldb) 
Process 24797 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step over
    frame #0: 0x0000000100000f4a int32`toPower_loop + 12
int32`toPower_loop:
->  0x100000f4a <+12>: popq   %rsi
    0x100000f4b <+13>: leaq   0x5(%rip), %r8            ; toPower1
    0x100000f52 <+20>: jmp    0x100000eef               ; times

int32`toPower1:
    0x100000f57 <+0>:  pushq  %rax
Target 0: (int32) stopped.
(lldb) 
Process 24797 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step over
    frame #0: 0x0000000100000f4b int32`toPower_loop + 13
int32`toPower_loop:
->  0x100000f4b <+13>: leaq   0x5(%rip), %r8            ; toPower1
    0x100000f52 <+20>: jmp    0x100000eef               ; times

int32`toPower1:
    0x100000f57 <+0>:  pushq  %rax

int32`toPower_next:
    0x100000f58 <+0>:  shrl   %ecx
Target 0: (int32) stopped.
(lldb) 
Process 24797 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step over
    frame #0: 0x0000000100000f52 int32`toPower_loop + 20
int32`toPower_loop:
->  0x100000f52 <+20>: jmp    0x100000eef               ; times

int32`toPower1:
    0x100000f57 <+0>:  pushq  %rax

int32`toPower_next:
    0x100000f58 <+0>:  shrl   %ecx
    0x100000f5a <+2>:  je     0x100000f75               ; toPower_done
Target 0: (int32) stopped.
(lldb) 
Process 24797 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
    frame #0: 0x0000000000000000
error: memory read failed for 0x0
Target 0: (int32) stopped.
(lldb) 

step inside _times

(lldb) n
Process 24894 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step over
    frame #0: 0x0000000100000ef1 int32`times + 2
int32`times:
->  0x100000ef1 <+2>:  imull  %esi, %eax
    0x100000ef4 <+5>:  jo     0x100000efd               ; times_overflow
    0x100000efa <+11>: jmpq   *%r8

int32`times_overflow:
    0x100000efd <+0>:  jmpq   *%r9
Target 0: (int32) stopped.
(lldb) reg read r8 r9 edi esi
      r8 = 0x0000000100000f57  int32`toPower1
      r9 = 0x0000000100000f7d  int32`toPower_overflow
     edi = 0x0290d741
     esi = 0x000019a1
(lldb) n
Process 24894 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step over
    frame #0: 0x0000000100000ef4 int32`times + 5
int32`times:
->  0x100000ef4 <+5>:  jo     0x100000efd               ; times_overflow
    0x100000efa <+11>: jmpq   *%r8

int32`times_overflow:
    0x100000efd <+0>:  jmpq   *%r9

int32`toPower:
    0x100000f00 <+0>:  movl   $0x0, %eax
Target 0: (int32) stopped.
(lldb) reg read r8 r9 edi esi
      r8 = 0x0000000100000f57  int32`toPower1
      r9 = 0x0000000100000f7d  int32`toPower_overflow
     edi = 0x0290d741
     esi = 0x000019a1
(lldb) n
Process 24894 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
    frame #0: 0x0000000000000000
error: memory read failed for 0x0
Target 0: (int32) stopped.
(lldb)