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-rw-r--r--util/alevt/hamm.c229
1 files changed, 229 insertions, 0 deletions
diff --git a/util/alevt/hamm.c b/util/alevt/hamm.c
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+#include "vt.h"
+#include "hamm.h"
+
+// table to decode hamm8/4 encoded bytes.
+// the low 4 bits are the (corrected) data bits
+// bit 8 is set if there was a single bit error
+// bit 12 is set if there was an uncorrectable error
+
+// the idea: you may add up to 15 words and get the
+// number of single bit errors in b8-b11 and the number
+// of double errors in b12-b15
+
+
+static unsigned short hammtab[256] =
+{
+ 0x0101, 0x100f, 0x0001, 0x0101, 0x100f, 0x0100, 0x0101, 0x100f,
+ 0x100f, 0x0102, 0x0101, 0x100f, 0x010a, 0x100f, 0x100f, 0x0107,
+ 0x100f, 0x0100, 0x0101, 0x100f, 0x0100, 0x0000, 0x100f, 0x0100,
+ 0x0106, 0x100f, 0x100f, 0x010b, 0x100f, 0x0100, 0x0103, 0x100f,
+ 0x100f, 0x010c, 0x0101, 0x100f, 0x0104, 0x100f, 0x100f, 0x0107,
+ 0x0106, 0x100f, 0x100f, 0x0107, 0x100f, 0x0107, 0x0107, 0x0007,
+ 0x0106, 0x100f, 0x100f, 0x0105, 0x100f, 0x0100, 0x010d, 0x100f,
+ 0x0006, 0x0106, 0x0106, 0x100f, 0x0106, 0x100f, 0x100f, 0x0107,
+ 0x100f, 0x0102, 0x0101, 0x100f, 0x0104, 0x100f, 0x100f, 0x0109,
+ 0x0102, 0x0002, 0x100f, 0x0102, 0x100f, 0x0102, 0x0103, 0x100f,
+ 0x0108, 0x100f, 0x100f, 0x0105, 0x100f, 0x0100, 0x0103, 0x100f,
+ 0x100f, 0x0102, 0x0103, 0x100f, 0x0103, 0x100f, 0x0003, 0x0103,
+ 0x0104, 0x100f, 0x100f, 0x0105, 0x0004, 0x0104, 0x0104, 0x100f,
+ 0x100f, 0x0102, 0x010f, 0x100f, 0x0104, 0x100f, 0x100f, 0x0107,
+ 0x100f, 0x0105, 0x0105, 0x0005, 0x0104, 0x100f, 0x100f, 0x0105,
+ 0x0106, 0x100f, 0x100f, 0x0105, 0x100f, 0x010e, 0x0103, 0x100f,
+ 0x100f, 0x010c, 0x0101, 0x100f, 0x010a, 0x100f, 0x100f, 0x0109,
+ 0x010a, 0x100f, 0x100f, 0x010b, 0x000a, 0x010a, 0x010a, 0x100f,
+ 0x0108, 0x100f, 0x100f, 0x010b, 0x100f, 0x0100, 0x010d, 0x100f,
+ 0x100f, 0x010b, 0x010b, 0x000b, 0x010a, 0x100f, 0x100f, 0x010b,
+ 0x010c, 0x000c, 0x100f, 0x010c, 0x100f, 0x010c, 0x010d, 0x100f,
+ 0x100f, 0x010c, 0x010f, 0x100f, 0x010a, 0x100f, 0x100f, 0x0107,
+ 0x100f, 0x010c, 0x010d, 0x100f, 0x010d, 0x100f, 0x000d, 0x010d,
+ 0x0106, 0x100f, 0x100f, 0x010b, 0x100f, 0x010e, 0x010d, 0x100f,
+ 0x0108, 0x100f, 0x100f, 0x0109, 0x100f, 0x0109, 0x0109, 0x0009,
+ 0x100f, 0x0102, 0x010f, 0x100f, 0x010a, 0x100f, 0x100f, 0x0109,
+ 0x0008, 0x0108, 0x0108, 0x100f, 0x0108, 0x100f, 0x100f, 0x0109,
+ 0x0108, 0x100f, 0x100f, 0x010b, 0x100f, 0x010e, 0x0103, 0x100f,
+ 0x100f, 0x010c, 0x010f, 0x100f, 0x0104, 0x100f, 0x100f, 0x0109,
+ 0x010f, 0x100f, 0x000f, 0x010f, 0x100f, 0x010e, 0x010f, 0x100f,
+ 0x0108, 0x100f, 0x100f, 0x0105, 0x100f, 0x010e, 0x010d, 0x100f,
+ 0x100f, 0x010e, 0x010f, 0x100f, 0x010e, 0x000e, 0x100f, 0x010e,
+};
+
+#if 0 // this information is contained in hamm24par bit 5
+// simple parity table (sum of 1 bits modulo 2)
+
+
+static char odd_parity[256] =
+{
+ 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
+ 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
+ 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
+ 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
+ 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
+ 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
+ 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
+ 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
+ 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
+ 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
+ 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
+ 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
+ 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
+ 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
+ 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
+ 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0
+};
+#endif
+
+// this table generates the parity checks for hamm24/18 decoding.
+// bit 0 is for test A, 1 for B, ...
+// thanks to R. Gancarz for this fine table *g*
+
+
+static char hamm24par[3][256] =
+{
+ { // parities of first byte
+ 0, 33, 34, 3, 35, 2, 1, 32, 36, 5, 6, 39, 7, 38, 37, 4,
+ 37, 4, 7, 38, 6, 39, 36, 5, 1, 32, 35, 2, 34, 3, 0, 33,
+ 38, 7, 4, 37, 5, 36, 39, 6, 2, 35, 32, 1, 33, 0, 3, 34,
+ 3, 34, 33, 0, 32, 1, 2, 35, 39, 6, 5, 36, 4, 37, 38, 7,
+ 39, 6, 5, 36, 4, 37, 38, 7, 3, 34, 33, 0, 32, 1, 2, 35,
+ 2, 35, 32, 1, 33, 0, 3, 34, 38, 7, 4, 37, 5, 36, 39, 6,
+ 1, 32, 35, 2, 34, 3, 0, 33, 37, 4, 7, 38, 6, 39, 36, 5,
+ 36, 5, 6, 39, 7, 38, 37, 4, 0, 33, 34, 3, 35, 2, 1, 32,
+ 40, 9, 10, 43, 11, 42, 41, 8, 12, 45, 46, 15, 47, 14, 13, 44,
+ 13, 44, 47, 14, 46, 15, 12, 45, 41, 8, 11, 42, 10, 43, 40, 9,
+ 14, 47, 44, 13, 45, 12, 15, 46, 42, 11, 8, 41, 9, 40, 43, 10,
+ 43, 10, 9, 40, 8, 41, 42, 11, 15, 46, 45, 12, 44, 13, 14, 47,
+ 15, 46, 45, 12, 44, 13, 14, 47, 43, 10, 9, 40, 8, 41, 42, 11,
+ 42, 11, 8, 41, 9, 40, 43, 10, 14, 47, 44, 13, 45, 12, 15, 46,
+ 41, 8, 11, 42, 10, 43, 40, 9, 13, 44, 47, 14, 46, 15, 12, 45,
+ 12, 45, 46, 15, 47, 14, 13, 44, 40, 9, 10, 43, 11, 42, 41, 8
+ }, { // parities of second byte
+ 0, 41, 42, 3, 43, 2, 1, 40, 44, 5, 6, 47, 7, 46, 45, 4,
+ 45, 4, 7, 46, 6, 47, 44, 5, 1, 40, 43, 2, 42, 3, 0, 41,
+ 46, 7, 4, 45, 5, 44, 47, 6, 2, 43, 40, 1, 41, 0, 3, 42,
+ 3, 42, 41, 0, 40, 1, 2, 43, 47, 6, 5, 44, 4, 45, 46, 7,
+ 47, 6, 5, 44, 4, 45, 46, 7, 3, 42, 41, 0, 40, 1, 2, 43,
+ 2, 43, 40, 1, 41, 0, 3, 42, 46, 7, 4, 45, 5, 44, 47, 6,
+ 1, 40, 43, 2, 42, 3, 0, 41, 45, 4, 7, 46, 6, 47, 44, 5,
+ 44, 5, 6, 47, 7, 46, 45, 4, 0, 41, 42, 3, 43, 2, 1, 40,
+ 48, 25, 26, 51, 27, 50, 49, 24, 28, 53, 54, 31, 55, 30, 29, 52,
+ 29, 52, 55, 30, 54, 31, 28, 53, 49, 24, 27, 50, 26, 51, 48, 25,
+ 30, 55, 52, 29, 53, 28, 31, 54, 50, 27, 24, 49, 25, 48, 51, 26,
+ 51, 26, 25, 48, 24, 49, 50, 27, 31, 54, 53, 28, 52, 29, 30, 55,
+ 31, 54, 53, 28, 52, 29, 30, 55, 51, 26, 25, 48, 24, 49, 50, 27,
+ 50, 27, 24, 49, 25, 48, 51, 26, 30, 55, 52, 29, 53, 28, 31, 54,
+ 49, 24, 27, 50, 26, 51, 48, 25, 29, 52, 55, 30, 54, 31, 28, 53,
+ 28, 53, 54, 31, 55, 30, 29, 52, 48, 25, 26, 51, 27, 50, 49, 24
+ }, { // parities of third byte
+ 63, 14, 13, 60, 12, 61, 62, 15, 11, 58, 57, 8, 56, 9, 10, 59,
+ 10, 59, 56, 9, 57, 8, 11, 58, 62, 15, 12, 61, 13, 60, 63, 14,
+ 9, 56, 59, 10, 58, 11, 8, 57, 61, 12, 15, 62, 14, 63, 60, 13,
+ 60, 13, 14, 63, 15, 62, 61, 12, 8, 57, 58, 11, 59, 10, 9, 56,
+ 8, 57, 58, 11, 59, 10, 9, 56, 60, 13, 14, 63, 15, 62, 61, 12,
+ 61, 12, 15, 62, 14, 63, 60, 13, 9, 56, 59, 10, 58, 11, 8, 57,
+ 62, 15, 12, 61, 13, 60, 63, 14, 10, 59, 56, 9, 57, 8, 11, 58,
+ 11, 58, 57, 8, 56, 9, 10, 59, 63, 14, 13, 60, 12, 61, 62, 15,
+ 31, 46, 45, 28, 44, 29, 30, 47, 43, 26, 25, 40, 24, 41, 42, 27,
+ 42, 27, 24, 41, 25, 40, 43, 26, 30, 47, 44, 29, 45, 28, 31, 46,
+ 41, 24, 27, 42, 26, 43, 40, 25, 29, 44, 47, 30, 46, 31, 28, 45,
+ 28, 45, 46, 31, 47, 30, 29, 44, 40, 25, 26, 43, 27, 42, 41, 24,
+ 40, 25, 26, 43, 27, 42, 41, 24, 28, 45, 46, 31, 47, 30, 29, 44,
+ 29, 44, 47, 30, 46, 31, 28, 45, 41, 24, 27, 42, 26, 43, 40, 25,
+ 30, 47, 44, 29, 45, 28, 31, 46, 42, 27, 24, 41, 25, 40, 43, 26,
+ 43, 26, 25, 40, 24, 41, 42, 27, 31, 46, 45, 28, 44, 29, 30, 47
+ }
+};
+
+// table to extract the lower 4 bit from hamm24/18 encoded bytes
+
+
+static char hamm24val[256] =
+{
+ 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1,
+ 2, 2, 2, 2, 3, 3, 3, 3, 2, 2, 2, 2, 3, 3, 3, 3,
+ 4, 4, 4, 4, 5, 5, 5, 5, 4, 4, 4, 4, 5, 5, 5, 5,
+ 6, 6, 6, 6, 7, 7, 7, 7, 6, 6, 6, 6, 7, 7, 7, 7,
+ 8, 8, 8, 8, 9, 9, 9, 9, 8, 8, 8, 8, 9, 9, 9, 9,
+ 10, 10, 10, 10, 11, 11, 11, 11, 10, 10, 10, 10, 11, 11, 11, 11,
+ 12, 12, 12, 12, 13, 13, 13, 13, 12, 12, 12, 12, 13, 13, 13, 13,
+ 14, 14, 14, 14, 15, 15, 15, 15, 14, 14, 14, 14, 15, 15, 15, 15,
+ 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1,
+ 2, 2, 2, 2, 3, 3, 3, 3, 2, 2, 2, 2, 3, 3, 3, 3,
+ 4, 4, 4, 4, 5, 5, 5, 5, 4, 4, 4, 4, 5, 5, 5, 5,
+ 6, 6, 6, 6, 7, 7, 7, 7, 6, 6, 6, 6, 7, 7, 7, 7,
+ 8, 8, 8, 8, 9, 9, 9, 9, 8, 8, 8, 8, 9, 9, 9, 9,
+ 10, 10, 10, 10, 11, 11, 11, 11, 10, 10, 10, 10, 11, 11, 11, 11,
+ 12, 12, 12, 12, 13, 13, 13, 13, 12, 12, 12, 12, 13, 13, 13, 13,
+ 14, 14, 14, 14, 15, 15, 15, 15, 14, 14, 14, 14, 15, 15, 15, 15
+};
+
+// mapping from parity checks made by table hamm24par to error
+// results return by hamm24.
+// (0 = no error, 0x0100 = single bit error, 0x1000 = double error)
+
+
+static short hamm24err[64] =
+{
+ 0x0000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000,
+ 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000,
+ 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000,
+ 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000,
+ 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100,
+ 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100,
+ 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100,
+ 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000,
+};
+
+// mapping from parity checks made by table hamm24par to faulty bit
+// in the decoded 18 bit word.
+
+
+static int hamm24cor[64] =
+{
+ 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000,
+ 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000,
+ 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000,
+ 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000,
+ 0x00000, 0x00000, 0x00000, 0x00001, 0x00000, 0x00002, 0x00004, 0x00008,
+ 0x00000, 0x00010, 0x00020, 0x00040, 0x00080, 0x00100, 0x00200, 0x00400,
+ 0x00000, 0x00800, 0x01000, 0x02000, 0x04000, 0x08000, 0x10000, 0x20000,
+ 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000,
+};
+
+
+int hamm8(u8 *p, int *err)
+{
+ int a = hammtab[p[0]];
+ *err += a;
+ return a & 15;
+}
+
+
+int hamm16(u8 *p, int *err)
+{
+ int a = hammtab[p[0]];
+ int b = hammtab[p[1]];
+ *err += a;
+ *err += b;
+ return (a & 15) | (b & 15) * 16;
+}
+
+
+int hamm24(u8 *p, int *err)
+{
+ int e = hamm24par[0][p[0]] ^ hamm24par[1][p[1]] ^ hamm24par[2][p[2]];
+ int x = hamm24val[p[0]] + p[1] % 128 * 16 + p[2] % 128 * 2048;
+ *err += hamm24err[e];
+ return x ^ hamm24cor[e];
+}
+
+
+int chk_parity(u8 *p, int n)
+{
+ int err;
+ for (err = 0; n--; p++)
+ if (hamm24par[0][*p] & 32)
+ *p &= 0x7f;
+ else
+ *p = BAD_CHAR, err++;
+ return err;
+}
generated by cgit v1.2.3 (git 2.25.1) at 2024-11-01 12:34:59 +0000