bitrev.h

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/*
 * Copyright (c) 2024 Tenstorrent AI ULC
 *
 * SPDX-License-Identifier: Apache-2.0
 */
 
#ifndef INCLUDE_TENSTORRENT_BITREV_H_
#define INCLUDE_TENSTORRENT_BITREV_H_
 
#include <stdint.h>
 
#ifdef __cplusplus
extern "C" {
#endif
 
static inline uint8_t bitrev4(uint8_t nibble)
{
        const uint8_t rev4[] = {0x0, 0x8, 0x4, 0xc, 0x2, 0xa, 0x6, 0xe,
                                0x1, 0x9, 0x5, 0xd, 0x3, 0xb, 0x7, 0xf};
 
        return rev4[nibble & 0xf];
}
 
static inline uint8_t bitrev8(uint8_t byte)
{
        return (bitrev4(byte) << 4) | bitrev4(byte >> 4);
}
 
static inline uint16_t bitrev16(uint16_t hword)
{
        return ((uint16_t)bitrev8(hword) << 8) | bitrev8(hword >> 8);
}
 
static inline uint32_t bitrev32(uint32_t word)
{
        return ((uint32_t)bitrev16(word) << 16) | bitrev16(word >> 16);
}
 
static inline uint64_t bitrev64(uint64_t dword)
{
        return ((uint64_t)bitrev32(dword) << 32) | bitrev32(dword >> 32);
}
 
/*
 * Note: arbitrary bit-widths can be reversed trivially by rounding
 * up to the nearest power of 2, performing the bit-reverals, and then
 * shifting.
 *
 * E.g. to reverse the 24 least-sigbnificant bits of a 32-bit word:
 *
 * static inline uint32_t bitrev24(uint32_t word) {
 *  return bitrev32(word) >> (32 - 24);
 * }
 */
 
#ifdef __cplusplus
}
#endif
 
#endif /* INCLUDE_TENSTORRENT_BITREV_H_ */