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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <cstdint>
#include <cstddef>
namespace search::diskindex {
/*
* Class containing Zc-encoded data in a memory buffer, typically
* docid deltas and skip information for posting lists.
*/
class ZcBuf
{
public:
uint8_t *_valI;
uint8_t *_valE;
uint8_t *_mallocStart;
size_t _mallocSize;
ZcBuf();
~ZcBuf();
static size_t zcSlack() { return 4; }
void clearReserve(size_t reserveSize);
void clear() { _valI = _mallocStart; }
size_t capacity() const { return _valE - _mallocStart; }
size_t size() const { return _valI - _mallocStart; }
size_t pos() const { return _valI - _mallocStart; }
void expand();
void maybeExpand() {
if (__builtin_expect(_valI >= _valE, false)) {
expand();
}
}
void encode(uint32_t num) {
for (;;) {
if (num < (1 << 7)) {
*_valI++ = num;
break;
}
*_valI++ = (num & ((1 << 7) - 1)) | (1 << 7);
num >>= 7;
}
maybeExpand();
}
uint32_t decode() {
uint32_t res;
uint8_t *valI = _valI;
if (__builtin_expect(valI[0] < (1 << 7), true)) {
res = valI[0];
valI += 1;
} else if (__builtin_expect(valI[1] < (1 << 7), true)) {
res = (valI[0] & ((1 << 7) - 1)) +
(valI[1] << 7);
valI += 2;
} else if (__builtin_expect(valI[2] < (1 << 7), true)) {
res = (valI[0] & ((1 << 7) - 1)) +
((valI[1] & ((1 << 7) - 1)) << 7) +
(valI[2] << 14);
valI += 3;
} else if (__builtin_expect(valI[3] < (1 << 7), true)) {
res = (valI[0] & ((1 << 7) - 1)) +
((valI[1] & ((1 << 7) - 1)) << 7) +
((valI[2] & ((1 << 7) - 1)) << 14) +
(valI[3] << 21);
valI += 4;
} else {
res = (valI[0] & ((1 << 7) - 1)) +
((valI[1] & ((1 << 7) - 1)) << 7) +
((valI[2] & ((1 << 7) - 1)) << 14) +
((valI[3] & ((1 << 7) - 1)) << 21) +
(valI[4] << 28);
valI += 5;
}
_valI = valI;
return res;
}
};
}
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