user: What would the C source look like for the assembly code provided here?

```asm
<qbase64_decode>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x140,%rsp
  mov    %rdi,-0x138(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x8(%rbp)
  xor    %eax,%eax
  movabs $0x4040404040404040,%rax
  movabs $0x4040404040404040,%rdx
  mov    %rax,-0x110(%rbp)
  mov    %rdx,-0x108(%rbp)
  mov    %rax,-0x100(%rbp)
  mov    %rdx,-0xf8(%rbp)
  movabs $0x4040404040404040,%rsi
  movabs $0x3f4040403e404040,%rdi
  mov    %rsi,-0xf0(%rbp)
  mov    %rdi,-0xe8(%rbp)
  movabs $0x3b3a393837363534,%rsi
  movabs $0x4040404040403d3c,%rdi
  mov    %rsi,-0xe0(%rbp)
  mov    %rdi,-0xd8(%rbp)
  movabs $0x605040302010040,%rsi
  movabs $0xe0d0c0b0a090807,%rdi
  mov    %rsi,-0xd0(%rbp)
  mov    %rdi,-0xc8(%rbp)
  movabs $0x161514131211100f,%rsi
  movabs $0x4040404040191817,%rdi
  mov    %rsi,-0xc0(%rbp)
  mov    %rdi,-0xb8(%rbp)
  movabs $0x201f1e1d1c1b1a40,%rsi
  movabs $0x2827262524232221,%rdi
  mov    %rsi,-0xb0(%rbp)
  mov    %rdi,-0xa8(%rbp)
  movabs $0x302f2e2d2c2b2a29,%rsi
  movabs $0x4040404040333231,%rdi
  mov    %rsi,-0xa0(%rbp)
  mov    %rdi,-0x98(%rbp)
  mov    %rax,-0x90(%rbp)
  mov    %rdx,-0x88(%rbp)
  mov    %rax,-0x80(%rbp)
  mov    %rdx,-0x78(%rbp)
  mov    %rax,-0x70(%rbp)
  mov    %rdx,-0x68(%rbp)
  mov    %rax,-0x60(%rbp)
  mov    %rdx,-0x58(%rbp)
  mov    %rax,-0x50(%rbp)
  mov    %rdx,-0x48(%rbp)
  mov    %rax,-0x40(%rbp)
  mov    %rdx,-0x38(%rbp)
  mov    %rax,-0x30(%rbp)
  mov    %rdx,-0x28(%rbp)
  mov    %rax,-0x20(%rbp)
  mov    %rdx,-0x18(%rbp)
  mov    -0x138(%rbp),%rax
  mov    %rax,-0x118(%rbp)
  movl   $0x0,-0x124(%rbp)
  movb   $0x0,-0x126(%rbp)
  mov    -0x138(%rbp),%rax
  mov    %rax,-0x120(%rbp)
  jmp    L7
L87:
  mov    -0x120(%rbp),%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  cltq
  movzbl -0x110(%rbp,%rax,1),%eax
  mov    %al,-0x125(%rbp)
  cmpb   $0x40,-0x125(%rbp)
  je     L24
  cmpl   $0x0,-0x124(%rbp)
  jne    L68
  addl   $0x1,-0x124(%rbp)
  jmp    L90
L68:
  cmpl   $0x1,-0x124(%rbp)
  jne    L93
  movsbl -0x126(%rbp),%eax
  shl    $0x2,%eax
  mov    %eax,%esi
  movzbl -0x125(%rbp),%eax
  sar    $0x4,%al
  mov    %eax,%ecx
  mov    -0x118(%rbp),%rax
  lea    0x1(%rax),%rdx
  mov    %rdx,-0x118(%rbp)
  or     %ecx,%esi
  mov    %esi,%edx
  mov    %dl,(%rax)
  addl   $0x1,-0x124(%rbp)
  jmp    L90
L93:
  cmpl   $0x2,-0x124(%rbp)
  jne    L76
  movsbl -0x126(%rbp),%eax
  shl    $0x4,%eax
  mov    %eax,%esi
  movzbl -0x125(%rbp),%eax
  sar    $0x2,%al
  mov    %eax,%ecx
  mov    -0x118(%rbp),%rax
  lea    0x1(%rax),%rdx
  mov    %rdx,-0x118(%rbp)
  or     %ecx,%esi
  mov    %esi,%edx
  mov    %dl,(%rax)
  addl   $0x1,-0x124(%rbp)
  jmp    L90
L76:
  movsbl -0x126(%rbp),%eax
  shl    $0x6,%eax
  mov    %eax,%ecx
  mov    -0x118(%rbp),%rax
  lea    0x1(%rax),%rdx
  mov    %rdx,-0x118(%rbp)
  or     -0x125(%rbp),%cl
  mov    %ecx,%edx
  mov    %dl,(%rax)
  movl   $0x0,-0x124(%rbp)
L90:
  movzbl -0x125(%rbp),%eax
  mov    %al,-0x126(%rbp)
  jmp    L46
L24:
  nop
L46:
  addq   $0x1,-0x120(%rbp)
L7:
  mov    -0x120(%rbp),%rax
  movzbl (%rax),%eax
  test   %al,%al
  jne    L87
  mov    -0x118(%rbp),%rax
  movb   $0x0,(%rax)
  mov    -0x118(%rbp),%rax
  sub    -0x138(%rbp),%rax
  mov    -0x8(%rbp),%rdx
  sub    %fs:0x28,%rdx
  je     L57
  call   <__stack_chk_fail@plt>
L57:
  leave
  ret
```

assistant: ```c
size_t qbase64_decode(char *str) {
  const char B64MAPTBL[16 * 16] = {64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 64, 64, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64, 64, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 64, 64, 64, 64, 64, 64, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64};
  char *pEncPt, *pBinPt = str;
  int nIdxOfFour = 0;
  char cLastByte = 0;
  for (pEncPt = str; *pEncPt != '\0'; pEncPt++) {
    char cByte = B64MAPTBL[(unsigned char)(*pEncPt)];
    if (cByte == 64)
      continue;
    if (nIdxOfFour == 0) {
      nIdxOfFour++;
    } else if (nIdxOfFour == 1) {
      *pBinPt++ = ((cLastByte << 2) | (cByte >> 4));
      nIdxOfFour++;
    } else if (nIdxOfFour == 2) {
      *pBinPt++ = ((cLastByte << 4) | (cByte >> 2));
      nIdxOfFour++;
    } else {
      *pBinPt++ = ((cLastByte << 6) | cByte);
      nIdxOfFour = 0;
    }
    cLastByte = cByte;
  }
  *pBinPt = '\0';
  return (pBinPt - str);
}
```