bitarithm.h

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/*
 * Copyright (C) 2017 Kaspar Schleiser <kaspar@schleiser.de>
 *               2014 Freie Universität Berlin
 *
 * This file is subject to the terms and conditions of the GNU Lesser
 * General Public License v2.1. See the file LICENSE in the top level
 * directory for more details.
 */
 
#ifndef BITARITHM_H
#define BITARITHM_H
 
#include <stdint.h>
 
#include "cpu_conf.h"
 
#ifdef __cplusplus
extern "C" {
#endif
 
#define SETBIT(val, bit)    val |= (bit)
 
#define CLRBIT(val, bit)    val &= (~(bit))
 
#ifndef BIT0
#define BIT0  0x00000001 
#define BIT1  0x00000002 
#define BIT2  0x00000004 
#define BIT3  0x00000008 
#define BIT4  0x00000010 
#define BIT5  0x00000020 
#define BIT6  0x00000040 
#define BIT7  0x00000080 
#define BIT8  0x00000100 
#define BIT9  0x00000200 
#endif
#ifndef BIT10
#define BIT10 0x00000400 
#define BIT11 0x00000800 
#define BIT12 0x00001000 
#define BIT13 0x00002000 
#define BIT14 0x00004000 
#define BIT15 0x00008000 
#endif
#ifndef BIT16
#define BIT16 0x00010000 
#define BIT17 0x00020000 
#define BIT18 0x00040000 
#define BIT19 0x00080000 
#define BIT20 0x00100000 
#define BIT21 0x00200000 
#define BIT22 0x00400000 
#define BIT23 0x00800000 
#define BIT24 0x01000000 
#define BIT25 0x02000000 
#define BIT26 0x04000000 
#define BIT27 0x08000000 
#define BIT28 0x10000000 
#define BIT29 0x20000000 
#define BIT30 0x40000000 
#define BIT31 0x80000000 
#endif
#define ARCH_32_BIT   (__INT_MAX__ == 2147483647) 
static inline unsigned bitarithm_msb(unsigned v);
 
static inline unsigned bitarithm_lsb(unsigned v);
 
unsigned bitarithm_bits_set(unsigned v);
 
#if ARCH_32_BIT
static inline uint8_t bitarithm_bits_set_u32(uint32_t v)
{
    return bitarithm_bits_set(v);
}
#else
uint8_t bitarithm_bits_set_u32(uint32_t v);
#endif
 
unsigned bitarith_msb_32bit_no_native_clz(unsigned v);
 
/* implementations */
 
static inline unsigned bitarithm_msb(unsigned v)
{
#if defined(BITARITHM_HAS_CLZ)
    return 8 * sizeof(v) - __builtin_clz(v) - 1;
#elif ARCH_32_BIT
    return bitarith_msb_32bit_no_native_clz(v);
#else
    unsigned r = 0;
    while (v >>= 1) { /* unroll for more speed... */
        ++r;
    }
    return r;
#endif
}
 
static inline uint8_t bitarithm_clzb(uint8_t x)
{
#if defined(BITARITHM_HAS_CLZ)
    /* clz operates on `unsigned int`, so `x` will be promoted to the size
       of an `unsigned int` */
    return __builtin_clz(x) - 8 * (sizeof(unsigned) - 1);
#else
    uint8_t l = 0;
    while (!(x & 0x80)) {
        ++l;
        x <<= 1;
    }
    return l;
#endif
}
 
extern const uint8_t bitarithm_MultiplyDeBruijnBitPosition[32];
 
static inline unsigned bitarithm_lsb(unsigned v)
#if defined(BITARITHM_LSB_BUILTIN)
{
    return __builtin_ffs(v) - 1;
}
#elif defined(BITARITHM_LSB_LOOKUP)
{
/* Source: http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup */
    /* cppcheck-suppress oppositeExpression
     * (reason: `x & -x` is a bit twiddling idiom to extract the LSB; the
     * check treats opposite arguments as indicator for poor copy-pasting
     * as e.g. `x + -x` or `x & ~x` don't make sense. ) */
    return bitarithm_MultiplyDeBruijnBitPosition[((uint32_t)((v & -v) * 0x077CB531U)) >>
                                       27];
}
#else
{
/* Source: http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogObvious */
    unsigned r = 0;
 
    while ((v & 0x01) == 0) {
        v >>= 1;
        r++;
    }
 
    return r;
}
#endif
 
static inline unsigned bitarithm_test_and_clear(unsigned state, uint8_t *index)
{
#if defined(BITARITHM_HAS_CLZ)
    *index = 8 * sizeof(state) - __builtin_clz(state) - 1;
    return state & ~(1 << *index);
#elif defined(BITARITHM_LSB_LOOKUP)
    /* Source: http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup */
    /* cppcheck-suppress oppositeExpression
     * (reason: `x & -x` is a bit twiddling idiom to extract the LSB; the
     * check treats opposite arguments as indicator for poor copy-pasting
     * as e.g. `x + -x` or `x & ~x` don't make sense. ) */
    uint32_t least_bit = state & -state;
    *index = bitarithm_MultiplyDeBruijnBitPosition[(least_bit * 0x077CB531U) >> 27];
    return state & ~least_bit;
#else
    while ((state & 1) == 0) {
        *index += 1;
        state >>= 1;
    }
    return state & ~1;
#endif
}
 
#ifdef __cplusplus
}
#endif
 
#endif /* BITARITHM_H */