Array merge sort

ams.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void sort(int *a, int n) {
  if (n <= 1) return;
  int m = (n + 1) / 2;
  sort(a, m);
  sort(a + m, n - m);
  int b[m];
  for (int i = 0; i < m; ++i) b[i] = a[i];
  int i = 0, ia = m, ib = 0;
  while (i < ia && ia < n && ib < m) a[i++] = a[ia] < b[ib] ? a[ia++] : b[ib++];
  while (ib < m) a[i++] = b[ib++];
}

// Optimization that avoids temp space and copying for sorted data.
void sort2(int *a, int n) {
  if (n <= 1) return;
  int m = (n + 1) / 2, k;
  sort2(a, m);
  sort2(a + m, n - m);
  for (k = 0; k < m && a[k] <= a[m]; ++k) ; // Find a[0..k-1] already sorted.
  int mb = m - k;
  if (mb == 0) return;
  int b[mb]; // Temp space for the unsorted chunk.
  for (int i = k; i < m; ++i) b[i - k] = a[i];
  int i = k, ia = m, ib = 0;
  while (i < ia && ia < n && ib < mb) a[i++] = a[ia] < b[ib] ? a[ia++] : b[ib++];
  while (ib < mb) a[i++] = b[ib++];
}

int main(void) {
  int n = 100, a[n];
  for (int i = 0; i < n; ++i) a[i] = rand();
  sort(a, n);
  for (int i = 0; i < n; ++i) printf("%d\n", a[i]);
  return 0;
}