round_up_pow2.h

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/*  round_up_pow2.h
 *
 *  Copyright (C) 2023 abxh
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *  See the file LICENSE included with this distribution for more
 *  information. */
 
#pragma once
 
#include <assert.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
 
static inline uint32_t round_up_pow2_32(uint32_t x)
{
    assert(0 < x && x <= UINT32_MAX / 2 + 1);
 
// Test for GCC >= 3.4.0
#if defined(__GNUC__) && (__GNUC__ > 3 || (__GNUC__ == 3 && (__GNUC_MINOR__ > 4 || __GNUC_MINOR__ == 4)))
 
    return x == 1U ? 1U : 1U << (32 - __builtin_clz(x - 1U));
 
#else
    x--;
    x |= x >> 1;
    x |= x >> 2;
    x |= x >> 4;
    x |= x >> 8;
    x |= x >> 16;
    x++;
    return x;
#endif
}
 
// vim: ft=c