Hexadecimal printing function in the style of xxd

hexdump.c

//          Copyright Jean Pierre Cimalando 2022.
// Distributed under the Boost Software License, Version 1.0.
//    (See accompanying file LICENSE or copy at
//          http://www.boost.org/LICENSE_1_0.txt)
//
// SPDX-License-Identifier: BSL-1.0

#include <stdio.h>
#include <stddef.h>

void hexdump(FILE *out, const void *data, size_t len)
{
    size_t i = 0;
    const char *hex = "0123456789abcdef";
    const unsigned char *src = (const unsigned char *)data;
    while (i < len) {
        size_t n = len - i;
        if (n > 16)
            n = 16;
        if (i > 0)
            fputc('\n', out);
        fprintf(out, "%08lx:", (unsigned long)i);
        for (size_t j = i; j < i + 16; ++j) {
            if ((j & 1) == 0)
                fputc(' ', out);
            if (j < i + n) {
                fputc(hex[src[j] >> 4], out);
                fputc(hex[src[j] & 15], out);
            }
            else {
                fputc(' ', out);
                fputc(' ', out);
            }
        }
        fputc(' ', out);
        fputc(' ', out);
        for (size_t j = i; j < i + n; ++j) {
            unsigned char c = src[j];
            fputc((c >= 0x20 && c < 0x80) ? c : '.', out);
        }
        i += n;
    }
    fputc('\n', out);
}