word.h

#ifndef WORD_H_
#define WORD_H_

#include <stdint.h>
#include <string.h>

typedef uint64_t uint64_t;

/* get byte from 64-bit Ascon word */
#define GETBYTE(x, i) ((uint8_t)((uint64_t)(x) >> (56 - 8 * (i))))

/* set byte in 64-bit Ascon word */
#define SETBYTE(b, i) ((uint64_t)(b) << (56 - 8 * (i)))

/* set padding byte in 64-bit Ascon word */
#define PAD(i) SETBYTE(0x80, i)

/* load bytes into 64-bit Ascon word */
static inline uint64_t LOADBYTES(const uint8_t* bytes, int n) {
  uint64_t x = 0;
  for (int i = 0; i < n; ++i) x |= SETBYTE(bytes[i], i);
  return x;
}

/* store bytes from 64-bit Ascon word */
static inline void STOREBYTES(uint8_t* bytes, uint64_t x, int n) {
  for (int i = 0; i < n; ++i) bytes[i] = GETBYTE(x, i);
}

/* clear bytes in 64-bit Ascon word */
static inline uint64_t CLEARBYTES(uint64_t x, int n) {
  for (int i = 0; i < n; ++i) x &= ~SETBYTE(0xff, i);
  return x;
}

#endif /* WORD_H_ */