Image Compressor — C source

/* Image compressor: quality search to a size budget — C (C11) port of the
 * image-compressor tool. C has no stdlib image codec, so the encoder is a
 * stand-in sized like a real one (libwebp WebPEncode / libjpeg plug in
 * here); the binary search over quality is the portable part. */

#include <stdio.h>

/* Stand-in for canvas -> WebP/JPEG encode: encoded size at a quality. */
typedef unsigned long (*encode_size_fn)(double quality);

/* Binary-search the quality until the encoded image fits the budget
 * (targetKb * 1024) — the core of the TS compressToBudget. Returns the
 * best fitting quality, or -1.0 when nothing fits (the TS fallback then
 * re-encodes once at the 0.05 floor). */
double compress_to_budget(encode_size_fn encode_size, unsigned long target_kb) {
    unsigned long budget = target_kb * 1024UL;
    double lo = 0.05, hi = 0.95, best = -1.0;
    while (lo <= hi) {
        double mid = (lo + hi) / 2.0;
        if (encode_size(mid) <= budget) {
            best = mid;        /* fits — try a higher quality */
            lo = mid + 0.05;
        } else {
            hi = mid - 0.05;   /* too big — step down */
        }
    }
    return best;
}

/* Deterministic stand-in codec: size grows ~linearly with quality. */
static unsigned long fake_encode(double q) {
    return (unsigned long)(12000.0 + 88000.0 * q);
}

int main(void) {
    /* The live tool decodes the bitmap, draws it to a canvas, then searches.
     * 50 KB budget: a mid-range quality fits just under it. */
    double q = compress_to_budget(fake_encode, 50);
    if (q < 0.0) {
        printf("no quality fits — falling back to the 0.05 floor\n");
        return 1;
    }
    printf("best quality %.2f -> %lu bytes\n", q, fake_encode(q));
    return 0;
}