user: Please show me the C implementation that matches the assembly code listed below:

```asm
<quicksort>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x48,%rsp
  mov    %edx,0x24(%rsp)
  test   %esi,%esi
  js     L49
  cmp    %esi,%edx
  jle    L49
  mov    %rdi,%r15
  mov    %esi,%r13d
L202:
  mov    0x24(%rsp),%edx
  mov    %r13d,%esi
  mov    %r15,%rdi
  call   <partition@plt>
  mov    %eax,0x28(%rsp)
  sub    $0x1,%eax
  mov    %eax,0x18(%rsp)
  cmp    %r13d,%eax
  jle    L11
  mov    %r13d,%r14d
  mov    %r15,%r13
L254:
  mov    0x18(%rsp),%edx
  mov    %r14d,%esi
  mov    %r13,%rdi
  call   <partition@plt>
  mov    %eax,0x2c(%rsp)
  sub    $0x1,%eax
  mov    %eax,0x1c(%rsp)
  cmp    %r14d,%eax
  jle    L92
  mov    %r14d,%eax
  mov    %r13,%r14
  mov    %eax,%r13d
L268:
  mov    0x1c(%rsp),%edx
  mov    %r13d,%esi
  mov    %r14,%rdi
  call   <partition@plt>
  mov    %eax,0x30(%rsp)
  sub    $0x1,%eax
  mov    %eax,0x20(%rsp)
  cmp    %r13d,%eax
  jle    L55
L168:
  mov    0x20(%rsp),%edx
  mov    %r13d,%esi
  mov    %r14,%rdi
  call   <partition@plt>
  lea    -0x1(%rax),%r12d
  mov    %eax,0x34(%rsp)
  cmp    %r13d,%r12d
  jle    L136
L179:
  mov    %r12d,%edx
  mov    %r13d,%esi
  mov    %r14,%rdi
  call   <partition@plt>
  lea    -0x1(%rax),%ebx
  mov    %eax,%ebp
  cmp    %r13d,%ebx
  jle    L81
  mov    %r12d,0x8(%rsp)
  mov    %r13d,%r15d
  mov    %ebx,%ebp
  mov    %r14,%r13
  mov    %eax,%r14d
L141:
  mov    %ebp,%edx
  mov    %r15d,%esi
  mov    %r13,%rdi
  call   <partition@plt>
  lea    -0x1(%rax),%ebx
  mov    %eax,0x14(%rsp)
  cmp    %r15d,%ebx
  jle    L147
  mov    %ebp,0xc(%rsp)
  mov    %ebx,0x10(%rsp)
  mov    %r13,%rbx
L144:
  mov    0x10(%rsp),%edx
  mov    %r15d,%esi
  mov    %rbx,%rdi
  call   <partition@plt>
  lea    -0x1(%rax),%r13d
  mov    %eax,0x38(%rsp)
  cmp    %r15d,%r13d
  jle    L64
  mov    %rbx,%rbp
  mov    %r13d,%ebx
L219:
  mov    %ebx,%edx
  mov    %r15d,%esi
  mov    %rbp,%rdi
  call   <partition@plt>
  lea    -0x1(%rax),%r13d
  mov    %eax,%r12d
  cmp    %r15d,%r13d
  jle    L94
  mov    %r13d,%ecx
L200:
  mov    %ecx,%edx
  mov    %r15d,%esi
  mov    %rbp,%rdi
  mov    %ecx,0x3c(%rsp)
  call   <partition@plt>
  mov    %r15d,%esi
  mov    %rbp,%rdi
  lea    -0x1(%rax),%edx
  mov    %eax,%r13d
  call   <quicksort>
  mov    0x3c(%rsp),%ecx
  lea    0x1(%r13),%r15d
  cmp    %r15d,%ecx
  jle    L94
  test   %r15d,%r15d
  jns    L200
L94:
  lea    0x1(%r12),%r15d
  cmp    %r15d,%ebx
  jle    L273
  test   %r15d,%r15d
  jns    L219
L273:
  mov    %rbp,%rbx
L64:
  mov    0x38(%rsp),%r15d
  add    $0x1,%r15d
  cmp    %r15d,0x10(%rsp)
  jle    L236
  test   %r15d,%r15d
  jns    L144
L236:
  mov    0xc(%rsp),%ebp
  mov    %rbx,%r13
L147:
  mov    0x14(%rsp),%r15d
  add    $0x1,%r15d
  cmp    %r15d,%ebp
  jle    L114
  test   %r15d,%r15d
  jns    L141
L114:
  mov    0x8(%rsp),%r12d
  mov    %r14d,%ebp
  mov    %r13,%r14
L81:
  lea    0x1(%rbp),%r13d
  cmp    %r13d,%r12d
  jle    L136
  test   %r13d,%r13d
  jns    L179
L136:
  mov    0x34(%rsp),%r13d
  add    $0x1,%r13d
  cmp    %r13d,0x20(%rsp)
  jle    L55
  test   %r13d,%r13d
  jns    L168
L55:
  mov    0x30(%rsp),%r13d
  add    $0x1,%r13d
  cmp    %r13d,0x1c(%rsp)
  jle    L231
  test   %r13d,%r13d
  jns    L268
L231:
  mov    %r14,%r13
L92:
  mov    0x2c(%rsp),%r14d
  add    $0x1,%r14d
  cmp    %r14d,0x18(%rsp)
  jle    L198
  test   %r14d,%r14d
  jns    L254
L198:
  mov    %r13,%r15
L11:
  mov    0x28(%rsp),%r13d
  add    $0x1,%r13d
  cmp    0x24(%rsp),%r13d
  jge    L49
  test   %r13d,%r13d
  jns    L202
L49:
  add    $0x48,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
```

assistant: ```c
void quicksort(int *arr, int start, int end) {
  if (start < end && start >= 0) {
    int q = partition(arr, start, end);
    quicksort(arr, start, q - 1);
    quicksort(arr, q + 1, end);
  }
}
```