Get the next multiple of an unsigned integer to assist with memory allocations and data alignment.

align_nums.c

/**
 * Simple program to find the next multiple of a number (AMD, NVIDIA, & Intel share 16-byte alignments for cache lines).
 *
 * gcc -std=c11 -Wall -Wextra -Werror -pedantic-errors align_nums.c -o align_nums
 */

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <time.h>


static inline bool is_aligned(const unsigned num, const unsigned alignment)
{
    return num % alignment == 0;
}



static inline unsigned next_multiple(const unsigned num, const unsigned alignment)
{
    return (num | (alignment-1)) + 1;
}



/*
static inline unsigned next_multiple_4(const unsigned num) {return (num | 0x03) + 1;}
static inline unsigned next_multiple_8(const unsigned num) {return (num | 0x07) + 1;}
static inline unsigned next_multiple_16(const unsigned num) {return (num | 0x0F) + 1;}
static inline unsigned next_multiple_32(const unsigned num) {return (num | 0x1F) + 1;}
static inline unsigned next_multiple_64(const unsigned num) {return (num | 0x3F) + 1;}
static inline unsigned next_multiple_128(const unsigned num) {return (num | 0x7F) + 1;}
static inline unsigned next_multiple_256(const unsigned num) {return (num | 0xFF) + 1;}
*/



int main()
{
    const unsigned ideal = 32;
    const unsigned maxNums = 20;
    unsigned randNums[maxNums];
    srand(time(NULL));
    
    printf("Generating random numbers... ");
    for (unsigned i = 0; i < maxNums; ++i)
    {
        randNums[i] = rand() % 513;
    }
    randNums[0] = ideal;
    printf("Done.\n");
    
    printf("Checking alignment of random numbers...\n");
    for (unsigned i = 0; i < maxNums; ++i)
    {
        const unsigned currentNum = randNums[i];
        
        printf("Validating alignment of %u: ", currentNum);
        
        if (!is_aligned(currentNum, ideal))
        {
            printf("Fail. Nearest Alignment is %u.\n", next_multiple(currentNum, ideal));
        }
        else
        {
            printf("Pass.\n");
        }
    }
    printf("Done.\n");
    
    return 0;
}