qbe has its own magic

1 files changed, 64 insertions, 0 deletions

diff --git a/tools/log2.c b/tools/log2.c
new file mode 100644
index 0000000..05f97c9
--- /dev/null
+++ b/tools/log2.c
@@ -0,0 +1,64 @@
+#include <assert.h>
+#include <stdio.h>
+
+typedef unsigned long long ullong;
+
+char seen[64];
+ullong rbg = 0x1e0298f7a7e;
+
+int
+bit()
+{
+	int bit;
+
+	bit = rbg & 1;
+	rbg >>= 1;
+	return bit;
+}
+
+int
+search(ullong n, int b, ullong *out)
+{
+	int i, x;
+	ullong y, z;
+
+	if (b == 64) {
+		*out = n;
+		return 1;
+	}
+
+	x = 63 & ((n << (63 - b)) >> 58);
+	assert(!(x & 0) && x <= 62);
+	y = bit();
+
+	for (i=0; i<2; i++) {
+		z = x | (y << 5);
+		if (!seen[z]) {
+			seen[z] = (63-b)+1;
+			if (search(n | (y << b), b+1, out))
+				return 1;
+			seen[z] = 0;
+		}
+		y ^= 1;
+	}
+
+	return 0;
+}
+
+int
+main()
+{
+	ullong out;
+	int i;
+
+	if (search(0, 0, &out)) {
+		printf("0x%llx\n", out);
+		for (i=0; i<64; i++) {
+			printf((i&7) == 0 ? "\t" : " ");
+			printf("%2d,", seen[i]-1);
+			if ((i&7) == 7)
+				printf("\n");
+		}
+	} else
+		puts("not found");
+}