source: azure_iot_hub/trunk/musl-1.1.18/src/stdio/fwrite.c@ 388

#include "stdio_impl.h"
#include <string.h>

size_t __fwritex(const unsigned char *restrict s, size_t l, FILE *restrict f)
{
        size_t i=0;

        if (!f->wend && __towrite(f)) return 0;

        if (l > f->wend - f->wpos) return f->write(f, s, l);

        if (f->lbf >= 0) {
                /* Match /^(.*\n|)/ */
                for (i=l; i && s[i-1] != '\n'; i--);
                if (i) {
                        size_t n = f->write(f, s, i);
                        if (n < i) return n;
                        s += i;
                        l -= i;
                }
        }

        memcpy(f->wpos, s, l);
        f->wpos += l;
        return l+i;
}

size_t fwrite(const void *restrict src, size_t size, size_t nmemb, FILE *restrict f)
{
        size_t k, l = size*nmemb;
        if (!size) nmemb = 0;
        FLOCK(f);
        k = __fwritex(src, l, f);
        FUNLOCK(f);
        return k==l ? nmemb : k/size;
}

#ifndef __c2__
weak_alias(fwrite, fwrite_unlocked);
#else
size_t fwrite_unlocked(const void *restrict src, size_t size, size_t nmemb, FILE *restrict f)
{
        return fwrite(src, size, nmemb, f);
}
#endif