entropy.c

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// SPDX-FileCopyrightText: 2021 deroad <wargio@libero.it>
// SPDX-License-Identifier: LGPL-3.0-only
 
#include "entropy.h"
#include <stdlib.h>
#include <math.h>
#include <rz_util/rz_assert.h>
 
bool rz_entropy_init(RzEntropy *ctx) {
    rz_return_val_if_fail(ctx, false);
    memset(ctx, 0, sizeof(RzEntropy));
    return true;
}
 
bool rz_entropy_update(RzEntropy *ctx, const ut8 *data, size_t len) {
    rz_return_val_if_fail(ctx && data, false);
    for (size_t i = 0; i < len; i++) {
        ctx->count[data[i]]++;
    }
    ctx->size += len;
    return true;
}
 
bool rz_entropy_final(ut8 *digest, RzEntropy *ctx, bool fraction) {
    rz_return_val_if_fail(ctx && digest, false);
    double p, entropy = 0.0;
    ut64 count;
    for (size_t i = 0; i < 256; i++) {
        count = ctx->count[i];
        if (count) {
            p = ((double)count) / ctx->size;
            entropy -= p * log2(p);
        }
    }
    if (fraction && ctx->size) {
        entropy /= log2((double)RZ_MIN(ctx->size, 256));
    }
    rz_write_be_double(digest, entropy);
    return true;
}