Updated xor magic

1 files changed, 23 insertions, 80 deletions

diff --git a/ptfformat.h b/ptfformat.h
index 30a82f9..dee8c1c 100644
--- a/ptfformat.h
+++ b/ptfformat.h
@@ -27,41 +27,18 @@
 #include <stdbool.h>
 #include <assert.h>
 
-static uint32_t baselut[16] = {
-	0xaaaaaaaa,
-	0xaa955555,
-	0xa9554aaa,
-	0xa552a955,
-	0xb56ad5aa,
-	0x95a95a95,
-	0x94a5294a,
-	0x9696b4b5,
-	0xd2d25a5a,
-	0xd24b6d25,
-	0xdb6db6da,
-	0xd9249b6d,
-	0xc9b64d92,
-	0xcd93264d,
-	0xccd99b32,
-	0xcccccccd
+static const uint32_t baselut[16] = {
+	0xaaaaaaaa, 0xaa955555, 0xa9554aaa, 0xa552a955,
+	0xb56ad5aa, 0x95a95a95, 0x94a5294a, 0x9696b4b5,
+	0xd2d25a5a, 0xd24b6d25, 0xdb6db6da, 0xd9249b6d,
+	0xc9b64d92, 0xcd93264d, 0xccd99b32, 0xcccccccd
 };
 
-static uint32_t hiseed[8] = {
-	0x00000000,
-	0x00b00000,
-	0x0b001000,
-	0x010b0b00,
-	0x10b0b010,
-	0xb01b01b0,
-	0xb101bb10,
-	0xbbbb1110
-};
-
-static uint32_t hixor4[4] = { // simple bit-map
-	0x000,
-	0x0a0,
-	0xa00,
-	0x0aa,
+static const uint32_t xorlut[16] = {
+	0x00000000, 0x00b00000, 0x0b001000, 0x010b0b00,
+	0x10b0b010, 0xb01b01b0, 0xb101bb10, 0xbbbb1110,
+	0xbbbb1111, 0xbb01bbb1, 0xb0bb0bb1, 0xbab0b0bb,
+	0xab0b0bab, 0xabaaba0b, 0xaabaa0ab, 0xaaaaaaab
 };
 
 class PTFFormat {
@@ -69,7 +46,7 @@ public:
 	PTFFormat();
 	~PTFFormat();
 
-	static uint32_t swapbytes32 (uint32_t v) {
+	static const uint32_t swapbytes32 (const uint32_t v) {
 		uint32_t rv = 0;
 		rv |= ((v >>  0) & 0xf) << 28;
 		rv |= ((v >>  4) & 0xf) << 24;
@@ -82,71 +59,37 @@ public:
 		return rv;
 	}
 
-	static uint32_t swapbytes16 (uint32_t v) {
-		uint32_t rv = 0;
-		rv |= ((v >>  0) & 0xf) << 12;
-		rv |= ((v >>  4) & 0xf) <<  8;
-		rv |= ((v >>  8) & 0xf) <<  4;
-		rv |= ((v >> 12) & 0xf) <<  0;
-		return rv;
-	}
-
-	static uint32_t mirror16 (uint32_t v) {
-		assert (0 == (v & 0xffff0000));
-		return (swapbytes16 (v) << 16) | v;
-	}
-
-	static uint32_t himap(int i) {
-		if (i & 4) {
-			return swapbytes16 (hixor4 [3 - (i & 3)] ^ 0xaaaa);
-		} else {
-			return hixor4 [i & 3];
-		}
-	}
-
-	static uint64_t gen_secret (int i) {
+	static const uint64_t gen_secret (int i) {
+		assert (i > 0 && i < 256);
 		int iwrap = i & 0x7f; // wrap at 0x80;
-		int idx; // mirror at 0x40;
-		uint32_t xor_lo = 0; // 0x40 flag
-		bool xorX = false; // mirror at 0x20
+		int idx;              // mirror at 0x40;
+		uint32_t xor_lo = 0;  // 0x40 flag
+		bool xor_20 = false;  // mirror at 0x20
 
 		if (iwrap & 0x40) {
-			idx = 0x80 - iwrap;
 			xor_lo = 0x1;
+			idx    = 0x80 - iwrap;
 		} else {
-			idx = iwrap;
+			idx    = iwrap;
 		}
 
-		int i16 = (idx >> 1) & 15;
-
+		int i16 = (idx >> 1) & 0xf;
 		if (idx & 0x20) {
 			i16 = 15 - i16;
-			xorX = true;
+			xor_20 = true;
 		}
 
 		uint32_t lo = baselut [i16];
+		uint32_t xk = xorlut  [i16];
 
-		int i08 = i16 & 7;
-
-		uint32_t xk;
-
-		if (i16 & 0x08) {
-			xk = hiseed  [7 - i08] ^ 1 ^ mirror16 (himap(i08));
-		} else {
-			xk = hiseed  [i08];
-		}
-
-		if (xorX) {
+		if (xor_20) {
 			lo ^= 0xaaaaaaab;
 			xk ^= 1;
 		}
-
-		uint32_t hi = swapbytes32(lo) ^ swapbytes32(xk);
-
+		uint32_t hi = swapbytes32 (lo) ^ swapbytes32 (xk);
 		return  ((uint64_t)hi << 32) | (lo ^ xor_lo);
 	}
 
-
 	/* Return values:	0            success
 				-1           could not open file as ptf
 	*/