user: What is the c source code of the assembly code below?

```asm
<reverse_sha256>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x48,%rsp
  mov    %rdi,0x10(%rsp)
  mov    %esi,0x2c(%rsp)
  mov    %edx,%ebp
  mov    %rcx,%r14
  mov    %rcx,%rdi
  call   <strlen@plt>
  mov    %eax,0x28(%rsp)
  mov    %ebp,%esi
  mov    %eax,%edi
  call   <pow@plt>
  mov    %eax,%ebx
  mov    %eax,0x1c(%rsp)
  mov    $0x41,%edi
  call   <malloc@plt>
  mov    %rax,0x8(%rsp)
  lea    0x1(%rbp),%edi
  call   <malloc@plt>
  mov    %rax,%r15
  movslq %ebp,%rax
  movb   $0x0,(%r15,%rax,1)
  test   %ebx,%ebx
  jle    L18
  lea    0x0(%rbp,%rbp,1),%eax
  mov    %eax,0x3c(%rsp)
  sub    $0x1,%eax
  mov    %eax,0x38(%rsp)
  movq   $0x0,0x30(%rsp)
  movl   $0x0,0x18(%rsp)
  movl   $0x0,0x4(%rsp)
  jmp    L103
L135:
  mov    %eax,%edi
  call   <log@plt>
  mov    %eax,%ebx
  mov    0x28(%rsp),%edi
  call   <log@plt>
  mov    %eax,%ecx
  mov    %ebx,%eax
  cltd
  idiv   %ecx
  mov    %eax,%edi
  call   <floor@plt>
  lea    0x1(%rax),%esi
  mov    0x3c(%rsp),%edi
  sub    %esi,%edi
  sub    $0x1,%edi
  mov    %ebp,%ecx
  sub    %esi,%ecx
  test   %ecx,%ecx
  jg     L25
  mov    0x18(%rsp),%ecx
  jmp    L46
L109:
  mov    0x20(%rsp),%r14
  lea    0x1(%r12),%edi
  call   <malloc@plt>
  mov    %rax,%rbx
  mov    %rax,0x30(%rsp)
  mov    %r12d,%edx
  mov    %r13,%rsi
  mov    %rax,%rdi
  call   <strncpy@plt>
  movslq %r12d,%r12
  movb   $0x0,(%rbx,%r12,1)
  movl   $0x1,0x18(%rsp)
L59:
  addl   $0x1,0x4(%rsp)
  mov    0x4(%rsp),%eax
  cmp    %eax,0x1c(%rsp)
  je     L147
L103:
  cmpl   $0x0,0x18(%rsp)
  jne    L59
  mov    0x4(%rsp),%eax
  test   %eax,%eax
  jne    L135
  mov    %ebp,%ecx
  mov    0x38(%rsp),%edi
  mov    0x4(%rsp),%esi
  test   %ebp,%ebp
  jle    L48
L25:
  mov    $0x0,%eax
L72:
  movzbl (%r14),%edx
  mov    %dl,(%r15,%rax,1)
  add    $0x1,%rax
  cmp    %eax,%ecx
  jg     L72
  test   %ecx,%ecx
  mov    $0x1,%eax
  cmovle %eax,%ecx
L46:
  mov    0x4(%rsp),%edx
  test   %edx,%edx
  je     L48
  cmp    %ecx,%ebp
  jle    L48
  add    $0x1,%ecx
  movslq %ecx,%rcx
  movslq %edi,%rdi
  lea    0x1(%r15,%rdi,1),%rdi
  mov    0x28(%rsp),%r8d
L133:
  mov    %edx,%eax
  cltd
  idiv   %r8d
  movslq %edx,%rdx
  movzbl (%r14,%rdx,1),%r9d
  mov    %rdi,%rdx
  sub    %rcx,%rdx
  mov    %r9b,(%rdx)
  mov    %eax,%edx
  test   %eax,%eax
  setne  %r9b
  cmp    %ecx,%ebp
  setg   %al
  add    $0x1,%rcx
  test   %al,%r9b
  jne    L133
L48:
  mov    0x2c(%rsp),%eax
  cmp    %eax,%esi
  cmovl  %eax,%esi
  mov    %ebp,%eax
  sub    %esi,%eax
  js     L59
  mov    $0x0,%ebx
  mov    %r14,0x20(%rsp)
  mov    %eax,%r14d
L134:
  mov    %ebp,%r12d
  sub    %ebx,%r12d
  lea    (%r15,%rbx,1),%r13
  mov    0x8(%rsp),%rdx
  mov    %r12d,%esi
  mov    %r13,%rdi
  call   <sha256@plt>
  mov    %eax,%esi
  mov    0x10(%rsp),%rdi
  call   <strcmp@plt>
  test   %rax,%rax
  je     L109
  add    $0x1,%rbx
  cmp    %ebx,%r14d
  jge    L134
  mov    0x20(%rsp),%r14
  jmp    L59
L18:
  movq   $0x0,0x30(%rsp)
L147:
  mov    0x8(%rsp),%rdi
  call   <free@plt>
  mov    %r15,%rdi
  call   <free@plt>
  mov    0x30(%rsp),%rax
  add    $0x48,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
```

assistant: ```c
char *reverse_sha256(const char *hash, int min_length, int max_length, const char *character_set) {
  int character_set_length = strlen(character_set), str_length;
  char *str_hash;
  char *str;
  int i, t, range;
  int64_t id, remainder;
  int64_t max_id = pow(character_set_length, max_length);
  int done = 0;
  char *result = NULL;
#pragma omp parallel private(id, i, t, range, remainder, str, str_hash)
  {
    str_hash = (char *)malloc(65 * sizeof(char));
    str = (char *)malloc((max_length + 1) * sizeof(char));
    str[max_length] = '\0';
#pragma omp for schedule(dynamic)
    for (id = 0; id < max_id; ++id) {
#pragma omp flush(done)
      if (done)
        continue;
      str_length = id == 0 ? 0 : (floor(log(id) / log(character_set_length)) + 1);
      t = 2 * max_length - str_length - 1;
      for (i = 0; i < max_length - str_length; ++i)
        str[i] = character_set[0];
      for (remainder = id; remainder && i < max_length; ++i) {
        str[t - i] = character_set[remainder % character_set_length];
        remainder /= character_set_length;
      }
      range = max_length - (str_length > min_length ? str_length : min_length);
      for (i = 0; i <= range; ++i) {
        if (strcmp(hash, sha256(str + i, max_length - i, str_hash)) == 0) {
          result = (char *)malloc((max_length - i + 1) * sizeof(char));
          strncpy(result, str + i, max_length - i);
          result[max_length - i] = '\0';
          done = 1;
          break;
        }
      }
    }
    free(str_hash);
    free(str);
  }
  return result;
}
```