82 lines
2.0 KiB
C
82 lines
2.0 KiB
C
#include <assert.h>
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#include "varint.h"
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static const char MSB = 0x80;
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static const char MSBALL = ~0x7F;
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static const unsigned long long N1 = 128; // 2 ^ 7
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static const unsigned long long N2 = 16384;
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static const unsigned long long N3 = 2097152;
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static const unsigned long long N4 = 268435456;
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static const unsigned long long N5 = 34359738368;
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static const unsigned long long N6 = 4398046511104;
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static const unsigned long long N7 = 562949953421312;
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static const unsigned long long N8 = 72057594037927936;
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static const unsigned long long N9 = 9223372036854775808U;
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int varint_encoding_length(unsigned long long n) {
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return (
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n < N1 ? 1
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: n < N2 ? 2
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: n < N3 ? 3
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: n < N4 ? 4
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: n < N5 ? 5
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: n < N6 ? 6
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: n < N7 ? 7
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: n < N8 ? 8
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: n < N9 ? 9
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: 10
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);
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}
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/**
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* Encode an unsigned long long into a varint
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* @param n the number to encode
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* @param buf where to put the results
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* @param len the length of buf
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* @param bytes the length written
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* @returns a pointer to the buf
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*/
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unsigned char* varint_encode(const unsigned long long n, unsigned char* buf, int len, size_t* bytes) {
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unsigned char* ptr = buf;
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unsigned long long copy = n;
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while (copy & MSBALL) {
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*(ptr++) = (copy & 0xFF) | MSB;
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copy = copy >> 7;
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assert((ptr - buf) < len);
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}
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*ptr = copy;
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if (bytes != NULL) *bytes = ptr - buf + 1;
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return buf;
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}
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/***
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* decode a varint
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* @param buf the buffer that contains the varint
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* @param len the length of the buffer
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* @param bytes number of bytes processed
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* @returns the value decoded
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*/
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unsigned long long varint_decode(const unsigned char* buf, int len, size_t* bytes) {
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unsigned long long result = 0;
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if (bytes != NULL) *bytes = 0;
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int bits = 0;
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const unsigned char* ptr = buf;
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unsigned long long ll;
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while (*ptr & MSB) {
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ll = *ptr;
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result += ((ll & 0x7F) << bits);
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ptr++;
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bits += 7;
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assert((ptr - buf) < len);
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}
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ll = *ptr;
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result += ((ll & 0x7F) << bits);
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if (bytes != NULL) *bytes = ptr - buf + 1;
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return result;
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}
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