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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 vespalib::compress {
class Integer {
public:
/**
* Will compress a positive integer to either 1,2 or 4 bytes
* @param n Number to compress
* @param destination Where to put the compressed number
* @return number of bytes used.
*/
static size_t compressPositive(uint64_t n, void *destination);
/**
* Will compress an integer to either 1,2 or 4 bytes
* @param n Number to compress
* @param destination Where to put the compressed number
* @return number of bytes used.
*/
static size_t compress(int64_t n, void *destination);
/**
* @param unsigned number to compute compressed size of in bytes.
* @return Will return the number of bytes this positive number will require
**/
static size_t compressedPositiveLength(uint64_t n) {
if (n < (0x1 << 6)) {
return 1;
} else if (n < (0x1 << 14)) {
return 2;
} else if ( n < (0x1 << 30)) {
return 4;
} else {
throw_too_big(n);
}
}
/**
* @param number to compute compressed size of in bytes.
* @return Will return the number of bytes this number will require
**/
static size_t compressedLength(int64_t n) {
if (n < 0) {
n = -n;
}
if (n < (0x1 << 5)) {
return 1;
} else if (n < (0x1 << 13)) {
return 2;
} else if ( n < (0x1 << 29)) {
return 4;
} else {
throw_too_big(n);
}
}
/**
* Will decompress an integer.
* @param pointer to buffer. pointer is automatically advanced.
* @return decompressed number
*/
static size_t decompress(int64_t & n, const void * srcv) {
const uint8_t * src = static_cast<const uint8_t *>(srcv);
const uint8_t c = src[0];
size_t numbytes;
if (__builtin_expect(c & 0x40, false)) {
if (c & 0x20) {
n = ((c & 0x1f) << 24) + (src[1] << 16) + (src[2] << 8) + src[3];
numbytes = 4;
} else {
n = ((c & 0x1f) << 8) + src[1];
numbytes = 2;
}
} else {
n = c & 0x1f;
numbytes = 1;
}
if (c & 0x80) {
n = -n;
}
return numbytes;
}
/**
* Will decompress a positive integer.
* @param pointer to buffer. pointer is automatically advanced.
* @return decompressed number
*/
static size_t decompressPositive(uint64_t & n, const void * srcv) {
const uint8_t * src = static_cast<const uint8_t *>(srcv);
const uint8_t c = src[0];
size_t numbytes;
if (c & 0x80) {
if (c & 0x40) {
n = ((c & 0x3f) << 24) + (src[1] << 16) + (src[2] << 8) + src[3];
numbytes = 4;
} else {
n = ((c & 0x3f) << 8) + src[1];
numbytes = 2;
}
} else {
n = c & 0x3f;
numbytes = 1;
}
return numbytes;
}
private:
[[ noreturn ]] static void throw_too_big(int64_t n);
[[ noreturn ]] static void throw_too_big(uint64_t n);
};
}
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