/*
- * Copyright (C) 2012, 2013
+ * Copyright (C) 2012, 2013, 2014
* Dale Weiler
* Wolfgang Bumiller
*
* SOFTWARE.
*/
#define GMQCC_PLATFORM_HEADER
+#include <stdlib.h>
#include "gmqcc.h"
#include "platform.h"
switch (typesize) {
case 1: return;
case 2:
- util_swap16((uint16_t*)_data, length>>1);
+ util_swap16((uint16_t*)_data, length);
return;
case 4:
- util_swap32((uint32_t*)_data, length>>2);
+ util_swap32((uint32_t*)_data, length);
return;
case 8:
- util_swap64((uint32_t*)_data, length>>3);
+ util_swap64((uint32_t*)_data, length<<1); /* swap64 operates on 32 bit words, thus scale to that length. */
return;
- default: exit(EXIT_FAILURE); /* please blow the fuck up! */
+ default:
+ con_err ("util_endianswap: I don't know how to swap a %u byte structure!\n", typesize);
+ exit(EXIT_FAILURE); /* please blow the fuck up! */
}
# endif
#endif
}
/*
-* CRC algorithms vary in the width of the polynomial, the value of said polynomial,
-* the initial value used for the register, weather the bits of each byte are reflected
-* before being processed, weather the algorithm itself feeds input bytes through the
-* register or XORs them with a byte from one end and then straight into the table, as
-* well as (but not limited to the idea of reflected versions) where the final register
-* value becomes reversed, and finally weather the value itself is used to XOR the final
-* register value. AS such you can already imagine how painfully annoying CRCs are,
-* of course we stand to target Quake, which expects it's certain set of rules for proper
-* calculation of a CRC.
+* Based On:
+* Slicing-by-8 algorithms by Michael E.
+* Kounavis and Frank L. Berry from Intel Corp.
+* http://www.intel.com/technology/comms/perfnet/download/CRC_generators.pdf
*
-* In most traditional CRC algorithms on uses a reflected table driven method where a value
-* or register is reflected if it's bits are swapped around it's center. For example:
-* take the bits 0101 is the 4-bit reflection of 1010, and respectfully 0011 would be the
-* reflection of 1100. Quake however expects a NON-Reflected CRC on the output, but still
-* requires a final XOR on the values (0xFFFF and 0x0000) this is a standard CCITT CRC-16
-* which I respectfully as a programmer don't agree with.
+* This code was made to be slightly less confusing with macros, which
+* I suppose is somewhat ironic.
*
-* So now you know what we target, and why we target it, despite how unsettling it may seem
-* but those are what Quake seems to request.
+* The code had to be changed for non reflected on the output register
+* since that's the method Quake uses.
+*
+* The code also had to be changed for CRC16, which is slightly harder
+* since the CRC32 method in the original Intel paper used a different
+* bit order convention.
+*
+* Notes about the table:
+* - It's exactly 4K in size
+* - 64 elements fit in a cache line
+* - can do 8 iterations unrolled 8 times for free
+* - The first 256 elements of the table are standard CRC16 table
+*
+* Table can be generated with the following utility:
*/
+#if 0
+#include <stdio.h>
+#include <stdint.h>
+int main(void) {
+ for (unsigned i = 0; i < 0x100; ++i) {
+ uint16_t x = i << 8;
+ for (int j = 0; j < 8; ++j)
+ x = (x << 1) ^ ((x & 0x8000) ? 0x1021 : 0);
+ tab[0][i] = x;
+ }
+ for (unsigned i = 0; i < 0x100; ++i) {
+ uint16_t c = tab[0][i];
+ for (unsigned j = 1; j < 8; ++j) {
+ c = tab[0][c >> 8] ^ (c << 8);
+ tab[j][i] = c;
+ }
+ }
+ printf("static const uint16_t util_crc16_table[8][256] = {");
+ for (int i = 0; i < 8; ++i) {
+ printf("{\n");
+ for (int j = 0; j < 0x100; ++j) {
+ printf((j & 7) ? " " : " ");
+ printf((j != 0x100-1) ? "0x%04X," : "0x%04X", tab[i][j]);
+ if ((j & 7) == 7)
+ printf("\n");
+ }
+ printf((i != 7) ? "}," : "}");
+ }
+ printf("};\n");
+ return 0;
+}
+#endif
+/*
+ * Non-Reflective version is present as well as a reference.
+ *
+ * TODO:
+ * combine the crc16 into u32s and mask off low high for byte order
+ * to make the arrays smaller.
+ */
static const uint16_t util_crc16_table[8][256] = {{
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7,
}};
/* Non - Reflected */
-uint16_t util_crc16(uint16_t current, const char *k, size_t len) {
+uint16_t util_crc16(uint16_t current, const char *GMQCC_RESTRICT k, size_t len) {
register uint16_t h = current;
/* don't load twice */
- uint8_t *GMQCC_RESTRICT data = (uint8_t *GMQCC_RESTRICT)k;
+ const uint8_t *GMQCC_RESTRICT data = (const uint8_t *GMQCC_RESTRICT)k;
size_t n;
/* deal with the first bytes as bytes until we reach an 8 byte boundary */
SELECT_DATA(1) ^
SELECT_DATA(0);
data += 8;
+ len -= 8;
}
+ #undef SELECT_BULK
+ #undef SELECT_DATA
+
/* deal with the rest with the byte method */
for (n = len & 7; n; --n)
h = (uint16_t)(h << 8) ^ (*util_crc16_table)[(h >> 8) ^ *data++];
return h;
}
-#if 0
-/* for reference: table generated with this: */
-/* compile with cc -std=c99 */
-int main(void) {
- for (unsigned i = 0; i < 0x100; ++i) {
- uint16_t x = i << 8;
- for (int j = 0; j < 8; ++j)
- x = (x << 1) ^ ((x & 0x8000) ? 0x1021 : 0);
- tab[0][i] = x;
- }
- for (unsigned i = 0; i < 0x100; ++i) {
- uint16_t c = tab[0][i];
- for (unsigned j = 1; j < 8; ++j) {
- c = tab[0][c >> 8] ^ (c << 8);
- tab[j][i] = c;
- }
- }
-
- printf("static const uint16_t util_crc16_table[8][256] = {");
- for (int i = 0; i < 8; ++i) {
- printf("{\n");
- for (int j = 0; j < 0x100; ++j) {
- printf((j & 7) ? " " : " ");
- printf((j != 0x100-1) ? "0x%04X," : "0x%04X", tab[i][j]);
- if ((j & 7) == 7)
- printf("\n");
- }
- printf((i != 7) ? "}," : "}");
- }
- printf("};\n");
- return 0;
-}
-#endif
-
/*
* modifier is the match to make and the transposition from it, while add is the upper-value that determines the
* transposition from uppercase to lower case.
*/
-static GMQCC_INLINE size_t util_strtransform(const char *in, char *out, size_t outsz, const char *mod, int add) {
+static size_t util_strtransform(const char *in, char *out, size_t outsz, const char *mod, int add) {
size_t sz = 1;
for (; *in && sz < outsz; ++in, ++out, ++sz) {
*out = (*in == mod[0])
projects / xonotic / gmqcc.git / blobdiff