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-rw-r--r--src/golay23.c332
1 files changed, 168 insertions, 164 deletions
diff --git a/src/golay23.c b/src/golay23.c
index 158a099..3b9790d 100644
--- a/src/golay23.c
+++ b/src/golay23.c
@@ -6,12 +6,13 @@
To test:
- src$ gcc golay23.c -o golay23 -Wall -O3 -DGOLAY23_UNITTEST && ./golay23
- src$ gcc golay23.c -o golay23 -Wall -O3 -DGOLAY23_UNITTEST -DRUN_TIME_TABLES && ./golay23
- src$ gcc golay23.c -o golay23 -Wall -O3 -DGOLAY23_UNITTEST -DNO_TABLES && ./golay23
+ src$ gcc golay23.c -o golay23 -Wall -O3 -DGOLAY23_UNITTEST && ./golay23
+ src$ gcc golay23.c -o golay23 -Wall -O3 -DGOLAY23_UNITTEST
+-DRUN_TIME_TABLES && ./golay23 src$ gcc golay23.c -o golay23 -Wall -O3
+-DGOLAY23_UNITTEST -DNO_TABLES && ./golay23
To generate tables:
- src$ gcc golay23.c -o golay23 -Wall -O3 -DGOLAY23_MAKETABLES && ./golay23
+ src$ gcc golay23.c -o golay23 -Wall -O3 -DGOLAY23_MAKETABLES && ./golay23
\*---------------------------------------------------------------------------*/
@@ -44,24 +45,25 @@ int static encoding_table[4096];
int static decoding_table[2048];
static int inited = 0;
#else
-//default is to use precomputed tables
-#include "golayenctable.h"
+// default is to use precomputed tables
#include "golaydectable.h"
+#include "golayenctable.h"
#endif
#endif
-//since we want to avoid bit-reversing inside syndrome() we bit-reverse the polynomial instead
-#define GOLAY_POLYNOMIAL 0xC75 //AE3 reversed
+// since we want to avoid bit-reversing inside syndrome() we bit-reverse the
+// polynomial instead
+#define GOLAY_POLYNOMIAL 0xC75 // AE3 reversed
int golay23_syndrome(int c) {
- //could probably be done slightly smarter, but works
- int x;
- for (x = 11; x >= 0; x--) {
- if (c & ((1<<11) << x)) {
- c ^= GOLAY_POLYNOMIAL << x;
- }
+ // could probably be done slightly smarter, but works
+ int x;
+ for (x = 11; x >= 0; x--) {
+ if (c & ((1 << 11) << x)) {
+ c ^= GOLAY_POLYNOMIAL << x;
}
- return c;
+ }
+ return c;
}
#ifdef __GNUC__
@@ -71,124 +73,124 @@ int golay23_syndrome(int c) {
#define popcount __popcnt
#else
static int popcount(unsigned int c) {
- int ret = 0;
- while (c) {
- if (c & 1) {
- ret++;
- }
- c >>= 1;
+ int ret = 0;
+ while (c) {
+ if (c & 1) {
+ ret++;
}
- return ret;
+ c >>= 1;
+ }
+ return ret;
}
#endif
#if defined(NO_TABLES) || defined(RUN_TIME_TABLES)
static int golay23_encode_no_tables(int c) {
- c <<= 11;
- return golay23_syndrome(c) | c;
+ c <<= 11;
+ return golay23_syndrome(c) | c;
}
#endif
#ifdef NO_TABLES
static int unrotate(unsigned int c, int x) {
- return ((c << x) & 0x7FFFFF) | (c >> (23 - x));
+ return ((c << x) & 0x7FFFFF) | (c >> (23 - x));
}
static int golay23_decode_no_tables(int c) {
- //TODO: optimize?
- int x;
- c = unrotate(c, 12);
-
- for (x = 0; x < 23; x++) {
- int t;
- int s = golay23_syndrome(c);
+ // TODO: optimize?
+ int x;
+ c = unrotate(c, 12);
- if (popcount(s) <= 3) {
- return unrotate(c ^ s, x) & 0xFFF;
- }
+ for (x = 0; x < 23; x++) {
+ int t;
+ int s = golay23_syndrome(c);
- for (t = 0; t < 23; t++) {
- int c2 = c ^ (1 << t);
- int s = golay23_syndrome(c2);
+ if (popcount(s) <= 3) {
+ return unrotate(c ^ s, x) & 0xFFF;
+ }
- if (popcount(s) <= 2) {
- return unrotate(c2 ^ s, x) & 0xFFF;
- }
- }
+ for (t = 0; t < 23; t++) {
+ int c2 = c ^ (1 << t);
+ int s = golay23_syndrome(c2);
- //rotate
- c = (c >> 1) | ((c & 1) << 22);
+ if (popcount(s) <= 2) {
+ return unrotate(c2 ^ s, x) & 0xFFF;
+ }
}
- //shouldn't reach here..
- assert("Something is wrong with golay23_decode_no_tables()..");
- return c & 0xFFF;
+ // rotate
+ c = (c >> 1) | ((c & 1) << 22);
+ }
+
+ // shouldn't reach here..
+ assert("Something is wrong with golay23_decode_no_tables()..");
+ return c & 0xFFF;
}
#endif
void golay23_init(void) {
#ifdef RUN_TIME_TABLES
- int x, y, z;
- inited = 1;
- for (x = 0; x < 4096; x++) {
- encoding_table[x] = golay23_encode_no_tables(x);
+ int x, y, z;
+ inited = 1;
+ for (x = 0; x < 4096; x++) {
+ encoding_table[x] = golay23_encode_no_tables(x);
+ }
+
+ decoding_table[0] = 0;
+ // 1-bit errors
+ for (x = 0; x < 23; x++) {
+ int d = 1 << x;
+ decoding_table[golay23_syndrome(d)] = d;
+ }
+ // 2-bit errors
+ for (x = 0; x < 22; x++) {
+ for (y = x + 1; y < 23; y++) {
+ int d = (1 << x) | (1 << y);
+ decoding_table[golay23_syndrome(d)] = d;
}
-
- decoding_table[0] = 0;
- //1-bit errors
- for (x = 0; x < 23; x++) {
- int d = 1<<x;
+ }
+ // 3-bit errors
+ for (x = 0; x < 21; x++) {
+ for (y = x + 1; y < 22; y++) {
+ for (z = y + 1; z < 23; z++) {
+ int d = (1 << x) | (1 << y) | (1 << z);
decoding_table[golay23_syndrome(d)] = d;
+ }
}
- //2-bit errors
- for (x = 0; x < 22; x++) {
- for (y = x+1; y < 23; y++) {
- int d = (1<<x) | (1<<y);
- decoding_table[golay23_syndrome(d)] = d;
- }
- }
- //3-bit errors
- for (x = 0; x < 21; x++) {
- for (y = x+1; y < 22; y++) {
- for (z = y+1; z < 23; z++) {
- int d = (1<<x) | (1<<y) | (1<<z);
- decoding_table[golay23_syndrome(d)] = d;
- }
- }
- }
+ }
#endif
}
-int golay23_encode(int c) {
- assert(c >= 0 && c <= 0xFFF);
+int golay23_encode(int c) {
+ assert(c >= 0 && c <= 0xFFF);
#ifdef RUN_TIME_TABLES
- assert(inited);
+ assert(inited);
#endif
#ifdef NO_TABLES
- return golay23_encode_no_tables(c);
+ return golay23_encode_no_tables(c);
#else
- return encoding_table[c];
+ return encoding_table[c];
#endif
}
-int golay23_decode(int c) {
- assert(c >= 0 && c <= 0x7FFFFF);
+int golay23_decode(int c) {
+ assert(c >= 0 && c <= 0x7FFFFF);
#ifdef RUN_TIME_TABLES
- assert(inited);
+ assert(inited);
#endif
#ifdef NO_TABLES
- //duplicate old golay23_decode()'s shift
- return unrotate(golay23_decode_no_tables(c), 11);
+ // duplicate old golay23_decode()'s shift
+ return unrotate(golay23_decode_no_tables(c), 11);
#else
- //message is shifted 11 places left in the return value
- return c ^ decoding_table[golay23_syndrome(c)];
+ // message is shifted 11 places left in the return value
+ return c ^ decoding_table[golay23_syndrome(c)];
#endif
}
-int golay23_count_errors(int recd_codeword, int corrected_codeword) {
- return popcount(recd_codeword ^ corrected_codeword);
+int golay23_count_errors(int recd_codeword, int corrected_codeword) {
+ return popcount(recd_codeword ^ corrected_codeword);
}
/**
@@ -199,113 +201,115 @@ int golay23_count_errors(int recd_codeword, int corrected_codeword) {
#include <stdio.h>
int main() {
- int x;
- //generate and dump
- golay23_init();
+ int x;
+ // generate and dump
+ golay23_init();
- FILE *enc = fopen("golayenctable.h", "w");
- FILE *dec = fopen("golaydectable.h", "w");
+ FILE *enc = fopen("golayenctable.h", "w");
+ FILE *dec = fopen("golaydectable.h", "w");
- fprintf(enc, "/* Generated by golay23.c -DGOLAY23_MAKETABLE */\n\
+ fprintf(enc,
+ "/* Generated by golay23.c -DGOLAY23_MAKETABLE */\n\
\n\
const int static encoding_table[]={\n");
- for (x = 0; x < 4096; x++) {
- fprintf(enc, x < 4095 ? " 0x%x,\n" : " 0x%x\n", encoding_table[x]);
- }
- fprintf(enc, "};\n");
+ for (x = 0; x < 4096; x++) {
+ fprintf(enc, x < 4095 ? " 0x%x,\n" : " 0x%x\n", encoding_table[x]);
+ }
+ fprintf(enc, "};\n");
- fprintf(dec, "/* Generated by golay23.c -DGOLAY23_MAKETABLE */\n\
+ fprintf(dec,
+ "/* Generated by golay23.c -DGOLAY23_MAKETABLE */\n\
\n\
const int static decoding_table[]={\n");
- for (x = 0; x < 2048; x++) {
- fprintf(dec, x < 2047 ? " 0x%x,\n" : " 0x%x\n", decoding_table[x]);
- }
- fprintf(dec, "};\n");
+ for (x = 0; x < 2048; x++) {
+ fprintf(dec, x < 2047 ? " 0x%x,\n" : " 0x%x\n", decoding_table[x]);
+ }
+ fprintf(dec, "};\n");
- fclose(enc);
- fclose(dec);
+ fclose(enc);
+ fclose(dec);
- return 0;
+ return 0;
}
#elif defined(GOLAY23_UNITTEST)
+#include <memory.h>
#include <stdio.h>
#include <stdlib.h>
-#include <memory.h>
int main() {
- int c;
+ int c;
+
+ golay23_init();
+
+ // keep track of whether every single codeword has been checked
+ char *checkmask = malloc(1 << 23);
+ memset(checkmask, 0, 1 << 23);
- golay23_init();
+ // step through all possible messages
+ for (c = 0; c < (1 << 12); c++) {
+ int g23 = golay23_encode(c);
+ int x, y, z;
+ checkmask[g23] = 1;
+ int c2 = golay23_decode(g23) >> 11;
- //keep track of whether every single codeword has been checked
- char *checkmask = malloc(1<<23);
- memset(checkmask, 0, 1<<23);
+ printf("%03x -> %06x %03x\n", c, g23, c2);
- //step through all possible messages
- for (c = 0; c < (1<<12); c++) {
- int g23 = golay23_encode(c);
- int x,y,z;
- checkmask[g23] = 1;
- int c2 = golay23_decode(g23) >> 11;
+ if (c != c2) {
+ printf("Bad!\n");
+ exit(1);
+ }
- printf("%03x -> %06x %03x\n", c, g23, c2);
+ // test the code by flipping every combination of one, two and three bits
+ for (x = 0; x < 23; x++) {
+ int flipped = g23 ^ (1 << x);
+ checkmask[flipped] = 1;
+ int c2 = golay23_decode(flipped) >> 11;
+ if (c != c2) {
+ printf("Bad!\n");
+
+ exit(1);
+ }
+ }
+ for (x = 0; x < 22; x++) {
+ for (y = x + 1; y < 23; y++) {
+ int flipped = g23 ^ (1 << x) ^ (1 << y);
+ checkmask[flipped] = 1;
+ int c2 = golay23_decode(flipped) >> 11;
if (c != c2) {
- printf("Bad!\n");
- exit(1);
- }
+ printf("Bad!\n");
- //test the code by flipping every combination of one, two and three bits
- for (x = 0; x < 23; x++) {
- int flipped = g23 ^ (1<<x);
- checkmask[flipped] = 1;
- int c2 = golay23_decode(flipped) >> 11;
- if (c != c2) {
- printf("Bad!\n");
-
- exit(1);
- }
- }
-
- for (x = 0; x < 22; x++) {
- for (y = x+1; y < 23; y++) {
- int flipped = g23 ^ (1<<x) ^ (1<<y);
- checkmask[flipped] = 1;
- int c2 = golay23_decode(flipped) >> 11;
- if (c != c2) {
- printf("Bad!\n");
-
- exit(1);
- }
- }
- }
-
- for (x = 0; x < 21; x++) {
- for (y = x+1; y < 22; y++) {
- for (z = y+1; z < 23; z++) {
- int flipped = g23 ^ (1<<x) ^ (1<<y) ^ (1<<z);
- checkmask[flipped] = 1;
- int c2 = golay23_decode(flipped) >> 11;
- if (c != c2) {
- printf("Bad!\n");
- exit(1);
- }
- }
- }
+ exit(1);
}
+ }
}
- //did we check every codeword?
- for (c = 0; c < (1<<23); c++) {
- if (checkmask[c] != 1) {
- printf("%06x unchecked!\n", c);
+ for (x = 0; x < 21; x++) {
+ for (y = x + 1; y < 22; y++) {
+ for (z = y + 1; z < 23; z++) {
+ int flipped = g23 ^ (1 << x) ^ (1 << y) ^ (1 << z);
+ checkmask[flipped] = 1;
+ int c2 = golay23_decode(flipped) >> 11;
+ if (c != c2) {
+ printf("Bad!\n");
exit(1);
+ }
}
+ }
+ }
+ }
+
+ // did we check every codeword?
+ for (c = 0; c < (1 << 23); c++) {
+ if (checkmask[c] != 1) {
+ printf("%06x unchecked!\n", c);
+ exit(1);
}
+ }
- printf("Everything checks out\n");
- free(checkmask);
- return 0;
+ printf("Everything checks out\n");
+ free(checkmask);
+ return 0;
}
#endif
generated by cgit v1.2.3 (git 2.46.0) at 2026-01-26 20:11:58 +0000