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

```asm
<salsa20_8>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x98,%rsp
  mov    %rdi,%r12
  mov    %fs:0x28,%rax
  mov    %rax,0x88(%rsp)
  xor    %eax,%eax
  lea    0x40(%rsp),%rdi
  mov    $0x40,%edx
  mov    %r12,%rsi
  call   <blkcpy@plt>
  mov    0x50(%rsp),%r11d
  mov    0x40(%rsp),%ebp
  mov    0x70(%rsp),%edx
  mov    0x60(%rsp),%ebx
  mov    0x64(%rsp),%r10d
  mov    0x54(%rsp),%ecx
  mov    0x44(%rsp),%eax
  mov    %eax,0x10(%rsp)
  mov    0x74(%rsp),%esi
  mov    0x78(%rsp),%r8d
  mov    0x68(%rsp),%r15d
  mov    0x58(%rsp),%r14d
  mov    0x48(%rsp),%eax
  mov    %eax,0x14(%rsp)
  mov    0x4c(%rsp),%eax
  mov    %eax,0x18(%rsp)
  mov    0x7c(%rsp),%eax
  mov    %eax,0x24(%rsp)
  mov    0x6c(%rsp),%eax
  mov    %eax,0x20(%rsp)
  mov    0x5c(%rsp),%eax
  mov    %eax,0x1c(%rsp)
  mov    $0x4,%r9d
  mov    %ebp,%edi
  mov    %r14d,%eax
  mov    %r11d,%ebp
  mov    %ecx,%r14d
  mov    %r10d,%r13d
  mov    %r9,0x30(%rsp)
  mov    %r15d,%r9d
  mov    %r12,0x38(%rsp)
  mov    %r8d,%r12d
L29:
  lea    (%rdx,%rdi,1),%ecx
  mov    %ecx,%r11d
  shl    $0x7,%r11d
  sar    $0x19,%ecx
  or     %ecx,%r11d
  xor    %ebp,%r11d
  lea    (%r11,%rdi,1),%ecx
  mov    %ecx,%r8d
  shl    $0x9,%r8d
  sar    $0x17,%ecx
  or     %ecx,%r8d
  xor    %ebx,%r8d
  mov    %r8d,%ebx
  lea    (%r11,%r8,1),%ecx
  mov    %ecx,%r8d
  shl    $0xd,%r8d
  sar    $0x13,%ecx
  or     %ecx,%r8d
  mov    %r8d,%ecx
  xor    %edx,%ecx
  mov    %ebx,0x28(%rsp)
  mov    %ebx,%edx
  mov    %ecx,0xc(%rsp)
  add    %ecx,%edx
  mov    %edx,%ebp
  shl    $0x12,%ebp
  sar    $0xe,%edx
  or     %edx,%ebp
  xor    %edi,%ebp
  mov    0x10(%rsp),%r15d
  lea    (%r15,%r14,1),%edx
  mov    %edx,%r10d
  shl    $0x7,%r10d
  sar    $0x19,%edx
  or     %edx,%r10d
  xor    %r13d,%r10d
  lea    (%r10,%r14,1),%edx
  mov    %edx,%edi
  shl    $0x9,%edi
  mov    %edi,%ecx
  sar    $0x17,%edx
  or     %edx,%ecx
  xor    %esi,%ecx
  lea    (%r10,%rcx,1),%edx
  mov    %edx,%ebx
  shl    $0xd,%ebx
  sar    $0x13,%edx
  or     %edx,%ebx
  xor    %r15d,%ebx
  mov    %ecx,0x2c(%rsp)
  lea    (%rcx,%rbx,1),%ecx
  mov    %ecx,%esi
  shl    $0x12,%esi
  mov    %esi,%edx
  sar    $0xe,%ecx
  or     %ecx,%edx
  xor    %r14d,%edx
  lea    (%r9,%rax,1),%ecx
  mov    %ecx,%r8d
  shl    $0x7,%r8d
  sar    $0x19,%ecx
  or     %ecx,%r8d
  xor    %r12d,%r8d
  lea    (%r8,%r9,1),%ecx
  mov    %ecx,%esi
  shl    $0x9,%esi
  mov    %esi,%edi
  sar    $0x17,%ecx
  or     %ecx,%edi
  xor    0x14(%rsp),%edi
  lea    (%r8,%rdi,1),%ecx
  mov    %ecx,%r14d
  shl    $0xd,%r14d
  sar    $0x13,%ecx
  or     %ecx,%r14d
  xor    %eax,%r14d
  lea    (%rdi,%r14,1),%eax
  mov    %eax,%r15d
  shl    $0x12,%r15d
  sar    $0xe,%eax
  or     %eax,%r15d
  xor    %r9d,%r15d
  mov    0x24(%rsp),%r13d
  mov    %r13d,%ecx
  mov    0x20(%rsp),%r12d
  add    %r12d,%ecx
  mov    %ecx,%eax
  shl    $0x7,%eax
  sar    $0x19,%ecx
  or     %ecx,%eax
  xor    0x18(%rsp),%eax
  lea    (%rax,%r13,1),%ecx
  mov    %ecx,%esi
  shl    $0x9,%esi
  sar    $0x17,%ecx
  or     %ecx,%esi
  xor    0x1c(%rsp),%esi
  lea    (%rax,%rsi,1),%ecx
  mov    %ecx,%r9d
  shl    $0xd,%r9d
  sar    $0x13,%ecx
  or     %ecx,%r9d
  xor    %r12d,%r9d
  lea    (%rsi,%r9,1),%r12d
  mov    %r12d,%ecx
  shl    $0x12,%ecx
  sar    $0xe,%r12d
  or     %r12d,%ecx
  xor    %r13d,%ecx
  lea    0x0(%rbp,%rax,1),%r12d
  mov    %r12d,%r13d
  shl    $0x7,%r13d
  sar    $0x19,%r12d
  or     %r12d,%r13d
  xor    %ebx,%r13d
  mov    %r13d,0x10(%rsp)
  lea    0x0(%rbp,%r13,1),%ebx
  mov    %ebx,%r12d
  shl    $0x9,%r12d
  sar    $0x17,%ebx
  or     %ebx,%r12d
  xor    %edi,%r12d
  mov    %r12d,0x14(%rsp)
  mov    %r13d,%edi
  mov    %r12d,%r13d
  add    %r12d,%edi
  mov    %edi,%ebx
  shl    $0xd,%ebx
  sar    $0x13,%edi
  or     %edi,%ebx
  mov    %ebx,%r12d
  xor    %eax,%r12d
  mov    %r12d,0x18(%rsp)
  mov    %r13d,%eax
  add    %r12d,%eax
  mov    %eax,%r13d
  shl    $0x12,%r13d
  mov    %r13d,%edi
  sar    $0xe,%eax
  or     %eax,%edi
  xor    %ebp,%edi
  lea    (%r11,%rdx,1),%ebx
  mov    %ebx,%eax
  shl    $0x7,%eax
  sar    $0x19,%ebx
  or     %ebx,%eax
  xor    %r14d,%eax
  lea    (%rdx,%rax,1),%ebx
  mov    %ebx,%ebp
  shl    $0x9,%ebp
  sar    $0x17,%ebx
  or     %ebx,%ebp
  xor    %esi,%ebp
  mov    %ebp,%r14d
  mov    %ebp,0x1c(%rsp)
  lea    (%rax,%rbp,1),%esi
  mov    %esi,%ebp
  shl    $0xd,%ebp
  sar    $0x13,%esi
  or     %esi,%ebp
  xor    %r11d,%ebp
  lea    (%r14,%rbp,1),%esi
  mov    %esi,%r11d
  shl    $0x12,%r11d
  sar    $0xe,%esi
  or     %esi,%r11d
  xor    %edx,%r11d
  mov    %r11d,%r14d
  lea    (%r10,%r15,1),%edx
  mov    %edx,%esi
  shl    $0x7,%esi
  sar    $0x19,%edx
  or     %edx,%esi
  xor    %r9d,%esi
  mov    %esi,0x20(%rsp)
  lea    (%r15,%rsi,1),%edx
  mov    %edx,%ebx
  shl    $0x9,%ebx
  sar    $0x17,%edx
  or     %edx,%ebx
  xor    0x28(%rsp),%ebx
  lea    (%rsi,%rbx,1),%edx
  mov    %edx,%r13d
  shl    $0xd,%r13d
  sar    $0x13,%edx
  or     %edx,%r13d
  xor    %r10d,%r13d
  lea    (%rbx,%r13,1),%edx
  mov    %edx,%r9d
  shl    $0x12,%r9d
  sar    $0xe,%edx
  or     %edx,%r9d
  xor    %r15d,%r9d
  lea    (%r8,%rcx,1),%esi
  mov    %esi,%edx
  shl    $0x7,%edx
  sar    $0x19,%esi
  or     %esi,%edx
  xor    0xc(%rsp),%edx
  lea    (%rcx,%rdx,1),%r10d
  mov    %r10d,%esi
  shl    $0x9,%esi
  sar    $0x17,%r10d
  or     %r10d,%esi
  xor    0x2c(%rsp),%esi
  lea    (%rdx,%rsi,1),%r10d
  mov    %r10d,%r12d
  shl    $0xd,%r12d
  sar    $0x13,%r10d
  or     %r10d,%r12d
  xor    %r8d,%r12d
  lea    (%rsi,%r12,1),%r8d
  mov    %r8d,%r10d
  shl    $0x12,%r10d
  sar    $0xe,%r8d
  or     %r8d,%r10d
  xor    %ecx,%r10d
  mov    %r10d,0x24(%rsp)
  subq   $0x1,0x30(%rsp)
  jne    L29
  mov    %ebp,%r11d
  mov    %edi,%ebp
  mov    %r14d,%edi
  mov    %eax,%r14d
  mov    %r9d,%r15d
  mov    %r12d,%r8d
  mov    0x30(%rsp),%r9
  mov    0x38(%rsp),%r12
  mov    0x10(%rsp),%eax
  mov    %eax,0x44(%rsp)
  mov    0x14(%rsp),%eax
  mov    %eax,0x48(%rsp)
  mov    0x18(%rsp),%eax
  mov    %eax,0x4c(%rsp)
  mov    %ebp,0x40(%rsp)
  mov    %r14d,0x58(%rsp)
  mov    0x1c(%rsp),%eax
  mov    %eax,0x5c(%rsp)
  mov    %r11d,0x50(%rsp)
  mov    %edi,0x54(%rsp)
  mov    0x20(%rsp),%eax
  mov    %eax,0x6c(%rsp)
  mov    %ebx,0x60(%rsp)
  mov    %r13d,0x64(%rsp)
  mov    %r15d,0x68(%rsp)
  mov    %edx,0x70(%rsp)
  mov    %esi,0x74(%rsp)
  mov    %r8d,0x78(%rsp)
  mov    0x24(%rsp),%eax
  mov    %eax,0x7c(%rsp)
L16:
  mov    0x40(%rsp,%r9,4),%eax
  add    %eax,(%r12,%r9,4)
  add    $0x1,%r9
  cmp    $0x10,%r9
  jne    L16
  mov    0x88(%rsp),%rax
  sub    %fs:0x28,%rax
  jne    L3
  add    $0x98,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L3:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
void salsa20_8(uint32_t B[16]) {
  uint32_t x[16];
  size_t i;
  blkcpy(x, B, 64);
  for (i = 0; i < 8; i += 2) {
    x[4] ^= (((x[0] + x[12]) << (7)) | ((x[0] + x[12]) >> (32 - (7))));
    x[8] ^= (((x[4] + x[0]) << (9)) | ((x[4] + x[0]) >> (32 - (9))));
    x[12] ^= (((x[8] + x[4]) << (13)) | ((x[8] + x[4]) >> (32 - (13))));
    x[0] ^= (((x[12] + x[8]) << (18)) | ((x[12] + x[8]) >> (32 - (18))));
    x[9] ^= (((x[5] + x[1]) << (7)) | ((x[5] + x[1]) >> (32 - (7))));
    x[13] ^= (((x[9] + x[5]) << (9)) | ((x[9] + x[5]) >> (32 - (9))));
    x[1] ^= (((x[13] + x[9]) << (13)) | ((x[13] + x[9]) >> (32 - (13))));
    x[5] ^= (((x[1] + x[13]) << (18)) | ((x[1] + x[13]) >> (32 - (18))));
    x[14] ^= (((x[10] + x[6]) << (7)) | ((x[10] + x[6]) >> (32 - (7))));
    x[2] ^= (((x[14] + x[10]) << (9)) | ((x[14] + x[10]) >> (32 - (9))));
    x[6] ^= (((x[2] + x[14]) << (13)) | ((x[2] + x[14]) >> (32 - (13))));
    x[10] ^= (((x[6] + x[2]) << (18)) | ((x[6] + x[2]) >> (32 - (18))));
    x[3] ^= (((x[15] + x[11]) << (7)) | ((x[15] + x[11]) >> (32 - (7))));
    x[7] ^= (((x[3] + x[15]) << (9)) | ((x[3] + x[15]) >> (32 - (9))));
    x[11] ^= (((x[7] + x[3]) << (13)) | ((x[7] + x[3]) >> (32 - (13))));
    x[15] ^= (((x[11] + x[7]) << (18)) | ((x[11] + x[7]) >> (32 - (18))));
    x[1] ^= (((x[0] + x[3]) << (7)) | ((x[0] + x[3]) >> (32 - (7))));
    x[2] ^= (((x[1] + x[0]) << (9)) | ((x[1] + x[0]) >> (32 - (9))));
    x[3] ^= (((x[2] + x[1]) << (13)) | ((x[2] + x[1]) >> (32 - (13))));
    x[0] ^= (((x[3] + x[2]) << (18)) | ((x[3] + x[2]) >> (32 - (18))));
    x[6] ^= (((x[5] + x[4]) << (7)) | ((x[5] + x[4]) >> (32 - (7))));
    x[7] ^= (((x[6] + x[5]) << (9)) | ((x[6] + x[5]) >> (32 - (9))));
    x[4] ^= (((x[7] + x[6]) << (13)) | ((x[7] + x[6]) >> (32 - (13))));
    x[5] ^= (((x[4] + x[7]) << (18)) | ((x[4] + x[7]) >> (32 - (18))));
    x[11] ^= (((x[10] + x[9]) << (7)) | ((x[10] + x[9]) >> (32 - (7))));
    x[8] ^= (((x[11] + x[10]) << (9)) | ((x[11] + x[10]) >> (32 - (9))));
    x[9] ^= (((x[8] + x[11]) << (13)) | ((x[8] + x[11]) >> (32 - (13))));
    x[10] ^= (((x[9] + x[8]) << (18)) | ((x[9] + x[8]) >> (32 - (18))));
    x[12] ^= (((x[15] + x[14]) << (7)) | ((x[15] + x[14]) >> (32 - (7))));
    x[13] ^= (((x[12] + x[15]) << (9)) | ((x[12] + x[15]) >> (32 - (9))));
    x[14] ^= (((x[13] + x[12]) << (13)) | ((x[13] + x[12]) >> (32 - (13))));
    x[15] ^= (((x[14] + x[13]) << (18)) | ((x[14] + x[13]) >> (32 - (18))));
  }
  for (i = 0; i < 16; i++)
    B[i] += x[i];
}
```