load.c

#include <stdlib.h>
#include "load.h"

// Return true if there is more to read from in.  This function is used only if
// a memory allocation or reallocation fails, or if the data fills limit.
static inline int more(FILE *in)
{
    return ungetc(getc(in), in) != EOF;
}

// See load.h for description.
int load(FILE *in, size_t limit, void **dat, size_t *size, size_t *len)
{
    // if no input limit, then set it to the maximum size_t value
    if (limit == 0)
        limit--;

    // no bytes read so far
    *len = 0;

    // assure that *dat has an allocation to read into
    if (*dat == NULL) {
        *size = (size_t)1 << 15;    // 32 KiB
        *dat = malloc(*size);
        if (*dat == NULL) {
            *size = 0;
            return more(in) ? -2 : 0;
        }
    }

    // read from in until no more input, the limit is reached, or out of memory
    for (;;) {
        // read as much as is available into the allocated space up to limit
        {
            size_t max = *size > limit ? limit : *size;
            *len += fread(*dat + *len, 1, max - *len, in);
            if (ferror(in))
                return -1;
            if (*len < max || *size >= limit)
                break;
        }

        // increase size to the next power of two, saturating to the maximum
        // size_t value
        {
            size_t reduce, bigger;
            reduce = *size;
            do {
                bigger = reduce;
                reduce &= reduce - 1;
            } while (reduce);
            bigger <<= 1;
            if (bigger == 0)
                bigger--;
            void *mem = realloc(*dat, bigger);
            if (mem == NULL)
                return more(in) ? -2 : 0;
            *dat = mem;
            *size = bigger;
        }
    }

    // return 0 on success, 1 if limit was reached with unread input
    return *len == limit && more(in) ? 1 : 0;
}