83 lines
1.8 KiB
C
83 lines
1.8 KiB
C
#include "config.h"
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#include <ccan/short_types/short_types.h>
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#include <common/descriptor_checksum.h>
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#include <stdlib.h>
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static const char CHECKSUM_CHARSET[] = "qpzry9x8gf2tvdw0s3jn54khce6mua7l";
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static const char INPUT_CHARSET[] =
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"0123456789()[],'/*abcdefgh@:$%{}"
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"IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~"
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"ijklmnopqrstuvwxyzABCDEFGH`#\"\\ ";
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static inline int charset_find(char ch) {
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for (size_t i = 0; i < sizeof(INPUT_CHARSET); i++) {
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if (INPUT_CHARSET[i] == ch)
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return i;
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}
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return -1;
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}
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static u64 polymod(u64 c, int val)
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{
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u8 c0 = c >> 35;
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c = ((c & 0x7ffffffff) << 5) ^ val;
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if (c0 & 1) c ^= 0xf5dee51989;
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if (c0 & 2) c ^= 0xa9fdca3312;
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if (c0 & 4) c ^= 0x1bab10e32d;
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if (c0 & 8) c ^= 0x3706b1677a;
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if (c0 & 16) c ^= 0x644d626ffd;
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return c;
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}
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bool descriptor_checksum(const char *descriptor, int desc_size,
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struct descriptor_checksum *checksum)
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{
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checksum->csum[0] = 0;
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int j;
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u64 c = 1;
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int cls = 0;
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int clscount = 0;
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for (int i = 0; i < desc_size; i++) {
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char ch = descriptor[i];
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int pos = charset_find(ch);
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if (pos == -1) {
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checksum->csum[0] = 0;
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return false;
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}
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/* Emit a symbol for the position inside the group, for every
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* character. */
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c = polymod(c, pos & 31);
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/* Accumulate the group numbers */
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cls = cls * 3 + (pos >> 5);
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if (++clscount == 3) {
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c = polymod(c, cls);
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cls = 0;
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clscount = 0;
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}
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}
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if (clscount > 0)
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c = polymod(c, cls);
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/* Shift further to determine the checksum. */
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for (j = 0; j < DESCRIPTOR_CHECKSUM_LENGTH; ++j)
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c = polymod(c, 0);
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/* Prevent appending zeroes from not affecting the checksum. */
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c ^= 1;
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for (j = 0; j < DESCRIPTOR_CHECKSUM_LENGTH; ++j)
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checksum->csum[j] = CHECKSUM_CHARSET[(c >> (5 * (7 - j))) & 31];
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checksum->csum[DESCRIPTOR_CHECKSUM_LENGTH] = 0;
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return true;
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}
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