user: Demonstrate the C code that generates the assembly output below:

```asm
<process_macros>:
  endbr64
  push   %r12
  push   %rbp
  mov    %rsi,%rbp
  push   %rbx
  mov    %rdi,%rbx
  call   <strlen@plt>
  test   %eax,%eax
  je     L179
  xor    %edx,%edx
  mov    $0x100,%r9d
  xor    %ecx,%ecx
  nopl   0x0(%rax)
L325:
  cmp    $0x5c,%cl
  movzbl (%rbx),%esi
  lea    -0x1(%rax),%edi
  setne  %r8b
  mov    %r8d,%r10d
  cmp    $0x5c,%sil
  jne    L409
  test   %r8b,%r8b
  je     L409
  sub    $0x2,%eax
  test   %edi,%edi
  je     L179
  movzbl 0x1(%rbx),%ecx
  lea    0x2(%rbx),%r11
  cmp    $0x2,%edx
  jne    L144
  test   %r9d,%r9d
  mov    %r11,%rbx
  setne  %r8b
  nopl   (%rax)
L405:
  cmp    $0x29,%cl
  sete   %dl
  cmp    $0x7d,%cl
  sete   %sil
  or     %esi,%edx
  xor    $0x1,%edx
  movzbl %dl,%edx
  add    %edx,%edx
L156:
  test   %eax,%eax
  je     L545
  test   %r8b,%r8b
  jne    L325
L545:
  test   %r9d,%r9d
  je     L369
L179:
  movb   $0x0,0x0(%rbp)
  pop    %rbx
  pop    %rbp
  pop    %r12
  ret
  nopw   0x0(%rax,%rax,1)
L409:
  add    $0x1,%rbx
  cmp    $0x2,%edx
  jne    L494
  test   %r9d,%r9d
  mov    %edi,%eax
  mov    %esi,%ecx
  setne  %r8b
  jmp    L405
  cs nopw 0x0(%rax,%rax,1)
L472:
  lea    0x1(%rdx),%rbx
  mov    $0x27,%ecx
L494:
  test   %edi,%edi
  setne  %al
  cmp    $0x27,%sil
  jne    L515
L402:
  test   %r10b,%r10b
  je     L515
  test   %r9d,%r9d
  je     L369
  test   %al,%al
  je     L545
  movzbl (%rbx),%ecx
  lea    0x1(%rbx),%rdx
  lea    -0x1(%rdi),%eax
  mov    $0x27,%esi
L463:
  test   %eax,%eax
  setne  %dil
  cmp    $0x27,%cl
  jne    L307
  cmp    $0x5c,%sil
  je     L307
  test   %r9d,%r9d
  setne  %r10b
  and    %dil,%r10b
  je     L545
  movzbl (%rdx),%esi
  lea    -0x1(%rax),%edi
  cmp    $0x5c,%sil
  jne    L472
  sub    $0x2,%eax
  test   %edi,%edi
  je     L179
  movzbl 0x1(%rdx),%ecx
  lea    0x2(%rdx),%r11
L526:
  lea    -0x1(%rax),%r8d
L424:
  test   %eax,%eax
  setne  %dl
  cmp    $0x24,%cl
  jne    L446
  cmp    $0x5c,%sil
  je     L446
  test   %r9d,%r9d
  je     L369
  test   %dl,%dl
  je     L545
  movzbl (%r11),%edx
  lea    -0x1(%rax),%ebx
  lea    0x1(%r11),%r12
  cmp    $0x5c,%dl
  jne    L229
  sub    $0x2,%eax
  test   %ebx,%ebx
  je     L179
  movzbl 0x1(%r11),%edx
  lea    0x2(%r11),%r12
  mov    %eax,%ebx
L229:
  cmp    $0x28,%dl
  sete   %r8b
  cmp    $0x7b,%dl
  sete   %al
  or     %al,%r8b
  jne    L28
  movb   $0x24,0x0(%rbp)
  cmp    $0x1,%r9d
  jne    L489
  add    $0x1,%rbp
L369:
  movb   $0x0,-0x1(%rbp)
  pop    %rbx
  pop    %rbp
  pop    %r12
  ret
  nopl   0x0(%rax)
L144:
  test   %edx,%edx
  je     L141
  test   %r9d,%r9d
  mov    %r11,%rbx
  setne  %r8b
  jmp    L156
  nop
L307:
  add    $0x1,%rbp
  mov    %cl,-0x1(%rbp)
  sub    $0x1,%r9d
  je     L369
  test   %dil,%dil
  je     L545
  add    $0x1,%rdx
  mov    %ecx,%esi
  sub    $0x1,%eax
  movzbl -0x1(%rdx),%ecx
  jmp    L463
  nopl   0x0(%rax,%rax,1)
L28:
  test   %ebx,%ebx
  je     L179
  movzbl (%r12),%ecx
  lea    -0x1(%rbx),%eax
  cmp    $0x5c,%cl
  sete   %sil
  cmp    $0x5c,%dl
  setne  %dl
  and    %dl,%sil
  je     L346
  lea    -0x2(%rbx),%edx
  test   %eax,%eax
  je     L179
  movzbl 0x1(%r12),%ecx
  lea    0x2(%r12),%rbx
  mov    %esi,%r8d
  mov    %edx,%eax
  jmp    L405
  cs nopw 0x0(%rax,%rax,1)
L446:
  add    $0x1,%rbp
  mov    %cl,-0x1(%rbp)
  sub    $0x1,%r9d
  je     L369
  test   %dl,%dl
  je     L545
  cmp    $0x5c,%cl
  movzbl (%r11),%esi
  mov    %r8d,%edi
  setne  %dl
  mov    %edx,%r10d
  cmp    $0x5c,%sil
  jne    L534
  test   %dl,%dl
  je     L534
  sub    $0x2,%eax
  test   %r8d,%r8d
  je     L179
  add    $0x2,%r11
  sub    $0x2,%r8d
  mov    $0x5c,%esi
  movzbl -0x1(%r11),%ecx
  jmp    L424
  xchg   %ax,%ax
L489:
  mov    %dl,0x1(%rbp)
  lea    0x2(%rbp),%r8
  sub    $0x2,%r9d
  test   %ebx,%ebx
  je     L272
  test   %r9d,%r9d
  je     L272
  cmp    $0x5c,%dl
  movzbl (%r12),%esi
  lea    -0x1(%rbx),%edi
  setne  %al
  mov    %eax,%r10d
  cmp    $0x5c,%sil
  jne    L15
  test   %al,%al
  je     L15
  lea    -0x2(%rbx),%eax
  test   %edi,%edi
  je     L539
  movzbl 0x1(%r12),%ecx
  lea    0x2(%r12),%r11
  mov    %r8,%rbp
  mov    $0x5c,%esi
  jmp    L526
  cs nopw 0x0(%rax,%rax,1)
L346:
  lea    0x1(%r12),%rbx
  jmp    L405
  nopw   0x0(%rax,%rax,1)
L534:
  test   %edi,%edi
  lea    0x1(%r11),%rbx
  setne  %al
  cmp    $0x27,%sil
  je     L402
  nopl   0x0(%rax,%rax,1)
L515:
  mov    %ecx,%edx
  mov    %edi,%eax
  mov    %esi,%ecx
  mov    %rbx,%r11
  mov    %edx,%esi
  jmp    L526
  nopl   0x0(%rax,%rax,1)
L15:
  lea    0x1(%r12),%rbx
  mov    %edx,%ecx
  mov    %r8,%rbp
  jmp    L494
  nop
L141:
  mov    $0x5c,%esi
  jmp    L526
L539:
  mov    %r8,%rbp
  jmp    L179
L272:
  mov    %r8,%rbp
  jmp    L545
```

assistant: ```c
void process_macros(const char *input, char *output) {
  char c, prev;
  const char *varname_start = NULL;
  int inputcnt = strlen((char *)input);
  int outputcnt = 256;
  int state = 0;
  prev = '\0';
  while (inputcnt && outputcnt) {
    c = *input++;
    inputcnt--;
    if (state != 3) {
      if ((c == '\\') && (prev != '\\')) {
        if (inputcnt-- == 0)
          break;
        prev = c;
        c = *input++;
      }
    }
    switch (state) {
    case 0:
      if ((c == '\'') && (prev != '\\')) {
        state = 3;
        break;
      }
      if ((c == '$') && (prev != '\\')) {
        state++;
      } else {
        *(output++) = c;
        outputcnt--;
      }
      break;
    case 1:
      if (c == '(' || c == '{') {
        state++;
        varname_start = input;
      } else {
        state = 0;
        *(output++) = '$';
        outputcnt--;
        if (outputcnt) {
          *(output++) = c;
          outputcnt--;
        }
      }
      break;
    case 2:
      if (c == ')' || c == '}') {
        int i;
        char envname[256], *envval = 0;
        int envcnt = input - varname_start - 1;
        for (i = 0; i < envcnt; i++) {
          envname[i] = varname_start[i];
        }
        envname[i] = 0;
        if (envval != NULL)
          while ((*envval) && outputcnt) {
            *(output++) = *(envval++);
            outputcnt--;
          }
        state = 0;
      }
      break;
    case 3:
      if ((c == '\'') && (prev != '\\')) {
        state = 0;
      } else {
        *(output++) = c;
        outputcnt--;
      }
      break;
    }
    prev = c;
  }
  if (outputcnt)
    *output = 0;
  else
    *(output - 1) = 0;
}
```