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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 <sys/types.h>
namespace vespalib {
/**
* @brief Bit fiddling class
*
* This class handles low level bit manipulation operations.
* - Fast bit reversal by table lookup.
**/
class Bits
{
public:
static uint8_t reverse(uint8_t v) { return _reverse[v]; }
static uint16_t reverse(uint16_t v) {
union { uint16_t v; uint8_t a[2]; } s, d;
s.v = v;
d.a[0] = _reverse[s.a[1]];
d.a[1] = _reverse[s.a[0]];
return d.v;
}
static uint32_t reverse(uint32_t v) {
union { uint32_t v; uint8_t a[4]; } s, d;
s.v = v;
d.a[0] = _reverse[s.a[3]];
d.a[1] = _reverse[s.a[2]];
d.a[2] = _reverse[s.a[1]];
d.a[3] = _reverse[s.a[0]];
return d.v;
}
static uint64_t reverse(uint64_t v) {
union { uint64_t v; uint8_t a[8]; } s, d;
s.v = v;
d.a[0] = _reverse[s.a[7]];
d.a[1] = _reverse[s.a[6]];
d.a[2] = _reverse[s.a[5]];
d.a[3] = _reverse[s.a[4]];
d.a[4] = _reverse[s.a[3]];
d.a[5] = _reverse[s.a[2]];
d.a[6] = _reverse[s.a[1]];
d.a[7] = _reverse[s.a[0]];
return d.v;
}
static void * reverse(void * v, size_t sz);
/**
Utility for other statically contructed objects to force correct init order."
**/
static void forceInitNow();
private:
class ReverseTableInit
{
public:
ReverseTableInit();
static uint8_t reverse(uint8_t v);
};
static uint8_t _reverse[256];
static ReverseTableInit _reverseTableInit;
};
}
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