Initial import

libc/alg/shuffle.h

@@ -0,0 +1,25 @@
+#ifndef COSMOPOLITAN_LIBC_RAND_SHUFFLE_H_
+#define COSMOPOLITAN_LIBC_RAND_SHUFFLE_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+#include "libc/bits/xchg.h"
+
+#if 0
+/**
+ * Fisher-Yates shuffle.
+ *
+ * @param R is a function like rand() → ≥0
+ * @param A is a typed array
+ * @param n is the number of items in A
+ * @see ARRAYLEN()
+ */
+#endif
+#define shuffle(R, A, n)                      \
+  do {                                        \
+    autotype(A) Array = (A);                  \
+    for (size_t i = (n)-1; i >= 1; --i) {     \
+      xchg(&Array[i], &Array[R() % (i + 1)]); \
+    }                                         \
+  } while (0)
+
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_RAND_SHUFFLE_H_ */