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fix the entrySelector calculation #178

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Merged
devongovett merged 4 commits into from
Nov 6, 2018
Merged

fix the entrySelector calculation #178

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f92e5c4
fix the entrySelector calculation
Pomax Oct 10, 2018
203a8f1
Math.pow instead of **
Pomax Nov 5, 2018
3f6700f
added a test
Pomax Nov 5, 2018
eba8a0b
cleanup
Pomax Nov 5, 2018
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7 changes: 5 additions & 2 deletions src/tables/directory.js
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Original file line number Diff line number Diff line change
Expand Up @@ -44,8 +44,11 @@ Directory.preEncode = function(stream) {
this.numTables = tables.length;
this.tables = tables;

this.searchRange = Math.floor(Math.log(this.numTables) / Math.LN2) * 16;
this.entrySelector = Math.floor(this.searchRange / Math.LN2);
let maxExponentFor2 = Math.floor((Math.log(this.numTables) / Math.LN2));
let maxPowerOf2 = Math.pow(2, maxExponentFor2);

this.searchRange = maxPowerOf2 * 16;
this.entrySelector = Math.log(maxPowerOf2) / Math.LN2;
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@Pomax Pomax Oct 10, 2018 •
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L47 guarantees that L49 is always* integer

*) up to the font-impossible value of Math.log(2**750), at least.

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@devongovett devongovett Nov 4, 2018

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I think you may need to add a Babel plugin for the exponentiation operator

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@Pomax Pomax Nov 5, 2018

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I'll rewrite it to Math.pow form - eventually IE will be dead and all those can be cleaned up, until then it's not really worth asking babel to do the conversion for.

this.rangeShift = this.numTables * 16 - this.searchRange;
};

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20 changes: 20 additions & 0 deletions test/directory.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
import fontkit from '../src';
import assert from 'assert';

describe('metadata', function() {
let font = fontkit.openSync(__dirname + '/data/OpenSans/OpenSans-Regular.ttf');

it('decodes SFNT directory values correctly', function() {
let dir = font.directory;
assert.equal(dir.numTables, 19);
assert.equal(dir.searchRange, 256);
assert.equal(dir.entrySelector, 4);
assert.equal(dir.rangeShift, 48);
});

it('numTables matches table collection', function() {
let dir = font.directory;
assert.equal(Object.keys(dir.tables).length, dir.numTables);
});

});