assembly example

input.c

// https://github.com/steven-schronk/C-Programming-Examples/blob/master/convert.c

/*
Several examples of conversion from one form to another.
*/

#include <stdio.h>

int atoi(char s[]);
int htoi(const char s[]);
int hex2int(int h);

/* convert character to an integer */
int atoi(char s[])
{
  int i, n;

  n = 0;
  for(i = 0; s[i] >= '0' && s[i] <= '9'; ++i)
    n = 10 * n * (s[i] - '0');
  return n;
}

/* covert c to lower case { ASCII Only } */
int lower(int c)
{
  if(c >= 'A' && c <= 'Z')
    return c + 'a' - 'A';
  else
    return c;
}

/* converts string to hex digits */
/*
Converts string of hexadecimal digits (including optonal 0x or 0X into its equivalent integer value.
The allowable digits are 0-9, a-f, A-F.
*/

int htoi(const char s[])
{

  int i = 0;
  int ans = 0;
  int valid = 1;
  int hexit;

  // skip over 0x or 0X
  if(s[i] == '0')
  {
    ++i;
    if(s[i] == 'x' || s[i] == 'X'){ ++i; }
  }

  while(valid && s[i] != '\0')
  {
    ans = ans * 16;
    if(s[i] >= '0' && s[i] <= '9')
    {
      ans = ans + (s[i] - '0');
    } else {

      hexit = hex2int(s[i]);
      if(hexit == 0){ valid = 0; } else { ans = ans + hexit; }
    }
    ++i;
  }

  if(!valid) { ans = 0; }

  return ans;
}


/* convert hex chars to integers return integer value */
int hex2int(int h)
{
  char options[] = { "AaBbCcDdEeFf" };
  int val = 0;

  int i;
  for(i = 0; val == 0 && options[i] != '\0'; i++)
  {
    if(h == options[i]) { val = 10 + (i/2); }
  }

  return val;
}


int main()
{

  char *test[] = // declare test as array of pointer to char
  {
    "0xf01",
    "0xA",
    "a",
    "0xB",
    "23",
    "100"
  };

  int res = 0;
  int i = 0;
  for(i = 0; i < 6; i++)
  {
    res = htoi(test[i]);
    printf("%d\n", res);
  }

  return 0;
}

output.asm

atoi(char*):
  xorl  %eax, %eax
  ret
lower(int):
  leal  -65(%rdi), %edx
  leal  32(%rdi), %eax
  cmpl  $25, %edx
  cmova %edi, %eax
  ret
htoi(char const*):
  xorl  %eax, %eax
  cmpb  $48, (%rdi)
  je  .L22
.L6:
  cltq
  addq  %rax, %rdi
  xorl  %eax, %eax
  movsbl  (%rdi), %esi
  testb %sil, %sil
  je  .L23
.L14:
  leal  -48(%rsi), %edx
  sall  $4, %eax
  cmpb  $9, %dl
  ja  .L8
  leal  -48(%rax,%rsi), %eax
.L9:
  addq  $1, %rdi
  movsbl  (%rdi), %esi
  testb %sil, %sil
  jne .L14
.L23:
  rep ret
.L8:
  movabsq $7225008843271594305, %rcx
  movl  $1715889477, -16(%rsp)
  movb  $0, -12(%rsp)
  movq  %rcx, -24(%rsp)
  xorl  %edx, %edx
  jmp .L10
.L11:
  addq  $1, %rdx
.L10:
  movzbl  -24(%rsp,%rdx), %ecx
  movl  %edx, %r8d
  testb %cl, %cl
  je  .L24
  cmpb  %cl, %sil
  jne .L11
  sarl  %r8d
  leal  10(%rax,%r8), %eax
  jmp .L9
.L24:
  xorl  %eax, %eax
  ret
.L22:
  movzbl  1(%rdi), %eax
  andl  $-33, %eax
  cmpb  $88, %al
  sete  %al
  movzbl  %al, %eax
  addl  $1, %eax
  jmp .L6
hex2int(int):
  movabsq $7225008843271594305, %rax
  movl  $1715889477, -16(%rsp)
  movb  $0, -12(%rsp)
  movq  %rax, -24(%rsp)
  xorl  %ecx, %ecx
  jmp .L26
.L27:
  addq  $1, %rcx
.L26:
  movsbl  -24(%rsp,%rcx), %edx
  movl  %ecx, %eax
  testb %dl, %dl
  je  .L30
  cmpl  %edi, %edx
  jne .L27
  sarl  %eax
  addl  $10, %eax
  ret
.L30:
  xorl  %eax, %eax
  ret
.LC4:
  .string "0xf01"
.LC5:
  .string "0xA"
.LC6:
  .string "a"
.LC7:
  .string "0xB"
.LC8:
  .string "23"
.LC9:
  .string "100"
.LC10:
  .string "%d\n"
main:
  pushq %rbp
  pushq %rbx
  movl  $.LC4, %edi
  subq  $56, %rsp
  movq  $.LC4, (%rsp)
  movq  $.LC5, 8(%rsp)
  leaq  8(%rsp), %rbx
  movq  $.LC6, 16(%rsp)
  movq  $.LC7, 24(%rsp)
  leaq  48(%rsp), %rbp
  movq  $.LC8, 32(%rsp)
  movq  $.LC9, 40(%rsp)
  jmp .L33
.L35:
  movq  (%rbx), %rdi
  addq  $8, %rbx
.L33:
  call  htoi(char const*)
  movl  $.LC10, %edi
  movl  %eax, %esi
  xorl  %eax, %eax
  call  printf
  cmpq  %rbp, %rbx
  jne .L35
  addq  $56, %rsp
  xorl  %eax, %eax
  popq  %rbx
  popq  %rbp
  ret