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Magic operation now calculates the entropy of each option and displays tooltips explaining the properties.

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This commit is contained in:
n1474335 2018-02-19 17:25:28 +00:00
parent 559741fd07
commit 56d33ea487
2 changed files with 50 additions and 10 deletions
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30
src/core/lib/Magic.js
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@ -173,6 +173,24 @@ class Magic {
return true;
}
/**
* Calculates the Shannon entropy of the input data.
*
* @returns {number}
*/
calcEntropy() {
let prob = this._freqDist(),
entropy = 0,
p;
for (let i = 0; i < prob.length; i++) {
p = prob[i] / 100;
if (p === 0) continue;
entropy += p * Math.log(p) / Math.log(2);
}
return -entropy;
}
/**
* Generate various simple brute-forced encodings of the data (trucated to 100 bytes).
*
@ -262,6 +280,7 @@ class Magic {
languageScores: this.detectLanguage(extLang),
fileType: this.detectFileType(),
isUTF8: this.isUTF8(),
entropy: this.calcEntropy(),
matchingOps: matchingOps,
useful: useful
});
@ -324,6 +343,10 @@ class Magic {
aScore += a.recipe.length;
bScore += b.recipe.length;
// Lower entropy is "better", so we add the entropy to the score
aScore += a.entropy;
bScore += b.entropy;
return aScore - bScore;
});
}
@ -351,12 +374,14 @@ class Magic {
}
/**
* Calculates the number of times each byte appears in the input
* Calculates the number of times each byte appears in the input as a percentage
*
* @private
* @returns {number[]}
*/
_freqDist() {
if (this.freqDist) return this.freqDist;
const len = this.inputBuffer.length;
let i = len,
counts = new Array(256).fill(0);
@ -367,9 +392,10 @@ class Magic {
counts[this.inputBuffer[i]]++;
}
return counts.map(c => {
this.freqDist = counts.map(c => {
return c / len * 100;
});
return this.freqDist;
}
/**