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

```asm
<rec_matmul>:
  endbr64
  push   %r15
  lea    (%rcx,%r8,1),%r15d
  push   %r14
  lea    (%r15,%r9,1),%eax
  push   %r13
  mov    %rdi,%r13
  push   %r12
  mov    %ecx,%r12d
  push   %rbp
  mov    %r9d,%ebp
  push   %rbx
  mov    %r8d,%ebx
  sub    $0x28,%rsp
  mov    %rsi,(%rsp)
  mov    0x68(%rsp),%r14d
  mov    %rdx,0x8(%rsp)
  cmp    $0x40,%eax
  jle    L99
  mov    0x8(%rsp),%rdx
  mov    (%rsp),%r13
  mov    %r14d,%r10d
  mov    %rdi,%r14
L72:
  cmp    %ebx,%r12d
  jl     L17
  cmp    %ebp,%ebx
  jl     L17
  push   %r10
  mov    0x68(%rsp),%eax
  mov    %r12d,%r15d
  mov    %ebp,%r9d
  sar    %r15d
  mov    %ebx,%r8d
  mov    %r14,%rdi
  mov    %r13,%rsi
  mov    %r15d,%ecx
  sub    %r15d,%r12d
  mov    %r10d,0x70(%rsp)
  push   %rax
  mov    %rdx,0x10(%rsp)
  call   <rec_matmul>
  imul   0x70(%rsp),%r15d
  mov    0x10(%rsp),%rdx
  pop    %r8
  pop    %r9
  mov    0x68(%rsp),%r10d
  movslq %r15d,%rax
  lea    (%r12,%rbx,1),%r15d
  shl    $0x2,%rax
  add    %rax,%rdx
  add    %rax,%r14
L29:
  lea    (%r15,%rbp,1),%eax
  cmp    $0x40,%eax
  jg     L72
  mov    %rdx,0x8(%rsp)
  mov    %r13,(%rsp)
  mov    %r14,%r13
  mov    %r10d,%r14d
L99:
  test   %r14d,%r14d
  jne    L52
  test   %r12d,%r12d
  jle    L165
  lea    -0x1(%rbx),%eax
  movslq 0x60(%rsp),%rsi
  xor    %r15d,%r15d
  movslq %ebp,%r11
  mov    %rax,0x10(%rsp)
  lea    0x4(%r13),%rax
  pxor   %xmm2,%xmm2
  mov    %rax,0x18(%rsp)
  shl    $0x2,%rsi
  xchg   %ax,%ax
L23:
  test   %ebp,%ebp
  jle    L105
  mov    0x18(%rsp),%rdi
  movslq %r15d,%rax
  mov    (%rsp),%r8
  lea    0x0(,%rax,4),%r9
  add    0x10(%rsp),%rax
  lea    0x0(%r13,%r9,1),%r10
  lea    (%rdi,%rax,4),%rcx
  add    0x8(%rsp),%r9
  xor    %edi,%edi
  nopl   (%rax)
L128:
  mov    %r8,%rdx
  mov    %r10,%rax
  movaps %xmm2,%xmm1
  test   %ebx,%ebx
  jle    L155
  nopl   (%rax)
L126:
  movss  (%rax),%xmm0
  mulss  (%rdx),%xmm0
  add    $0x4,%rax
  add    %rsi,%rdx
  addss  %xmm0,%xmm1
  cmp    %rcx,%rax
  jne    L126
L155:
  movss  %xmm1,(%r9,%rdi,4)
  add    $0x1,%rdi
  add    $0x4,%r8
  cmp    %r11,%rdi
  jne    L128
L105:
  add    $0x1,%r14d
  add    0x60(%rsp),%r15d
  cmp    %r12d,%r14d
  jne    L23
L165:
  add    $0x28,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L17:
  cmp    %ebp,%r12d
  mov    %ebp,%eax
  cmovge %r12d,%eax
  cmp    %ebx,%eax
  jg     L103
  push   %r10
  mov    0x68(%rsp),%eax
  mov    %ebx,%r15d
  mov    %r13,%rsi
  sar    %r15d
  mov    %r14,%rdi
  mov    %ebp,%r9d
  mov    %r12d,%ecx
  push   %rax
  mov    %r15d,%r8d
  sub    %r15d,%ebx
  mov    %rdx,0x10(%rsp)
  call   <rec_matmul>
  mov    0x70(%rsp),%eax
  mov    $0x1,%r10d
  pop    %rsi
  pop    %rdi
  mov    (%rsp),%rdx
  imul   %r15d,%eax
  movslq %r15d,%r15
  lea    (%r14,%r15,4),%r14
  lea    (%r12,%rbx,1),%r15d
  cltq
  lea    0x0(%r13,%rax,4),%r13
  jmp    L29
L103:
  push   %r10
  mov    0x68(%rsp),%eax
  mov    %ebp,%r9d
  mov    %r12d,%ecx
  sar    %r9d
  mov    %r13,%rsi
  mov    %ebx,%r8d
  mov    %r14,%rdi
  mov    %r10d,0x70(%rsp)
  push   %rax
  mov    %rdx,0x10(%rsp)
  mov    %r9d,0x18(%rsp)
  call   <rec_matmul>
  movslq 0x18(%rsp),%rax
  mov    0x10(%rsp),%rdx
  sub    %eax,%ebp
  shl    $0x2,%rax
  add    %rax,%rdx
  add    %rax,%r13
  pop    %rax
  pop    %rcx
  mov    0x68(%rsp),%r10d
  jmp    L29
L52:
  test   %r12d,%r12d
  jle    L165
  lea    -0x1(%rbx),%eax
  movslq 0x60(%rsp),%rsi
  xor    %r15d,%r15d
  xor    %r14d,%r14d
  mov    %rax,0x10(%rsp)
  lea    0x4(%r13),%rax
  movslq %ebp,%r11
  pxor   %xmm2,%xmm2
  mov    %rax,0x18(%rsp)
  shl    $0x2,%rsi
  nopl   0x0(%rax,%rax,1)
L94:
  test   %ebp,%ebp
  jle    L142
  mov    0x18(%rsp),%rdi
  movslq %r15d,%rax
  mov    (%rsp),%r8
  lea    0x0(,%rax,4),%r9
  add    0x10(%rsp),%rax
  lea    0x0(%r13,%r9,1),%r10
  lea    (%rdi,%rax,4),%rcx
  add    0x8(%rsp),%r9
  xor    %edi,%edi
  nopl   (%rax)
L97:
  mov    %r8,%rdx
  mov    %r10,%rax
  movaps %xmm2,%xmm1
  test   %ebx,%ebx
  jle    L70
  nopl   (%rax)
L175:
  movss  (%rax),%xmm0
  mulss  (%rdx),%xmm0
  add    $0x4,%rax
  add    %rsi,%rdx
  addss  %xmm0,%xmm1
  cmp    %rax,%rcx
  jne    L175
L70:
  addss  (%r9,%rdi,4),%xmm1
  add    $0x4,%r8
  movss  %xmm1,(%r9,%rdi,4)
  add    $0x1,%rdi
  cmp    %rdi,%r11
  jne    L97
L142:
  add    $0x1,%r14d
  add    0x60(%rsp),%r15d
  cmp    %r12d,%r14d
  jne    L94
  add    $0x28,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
```

assistant: ```c
void rec_matmul(float *A, float *B, float *C, int m, int n, int p, int ld, int add) {
  if ((m + n + p) <= 64) {
    int i, j, k;
    if (add) {
      for (i = 0; i < m; i++)
        for (k = 0; k < p; k++) {
          float c = 0.0;
          for (j = 0; j < n; j++)
            c += A[i * ld + j] * B[j * ld + k];
          C[i * ld + k] += c;
        }
    } else {
      for (i = 0; i < m; i++)
        for (k = 0; k < p; k++) {
          float c = 0.0;
          for (j = 0; j < n; j++)
            c += A[i * ld + j] * B[j * ld + k];
          C[i * ld + k] = c;
        }
    }
  } else if (m >= n && n >= p) {
    int m1 = m >> 1;
    rec_matmul(A, B, C, m1, n, p, ld, add);
    rec_matmul(A + m1 * ld, B, C + m1 * ld, m - m1, n, p, ld, add);
  } else if (n >= m && n >= p) {
    int n1 = n >> 1;
    rec_matmul(A, B, C, m, n1, p, ld, add);
    rec_matmul(A + n1, B + n1 * ld, C, m, n - n1, p, ld, 1);
  } else {
    int p1 = p >> 1;
    rec_matmul(A, B, C, m, n, p1, ld, add);
    rec_matmul(A, B + p1, C + p1, m, n, p - p1, ld, add);
  }
}
```