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compare buffer bytes directly for faster detection #70

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merged 2 commits into from
Dec 6, 2020
Merged

compare buffer bytes directly for faster detection #70

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188c251
reduce number of benchmark cases
mgartner Dec 6, 2020
cd936ec
compare buffer bytes directly for faster detection
mgartner Dec 6, 2020
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7 changes: 4 additions & 3 deletions bench/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -28,9 +28,10 @@ const ONE_BILLION = 1000000000

const fixtures = path.resolve(__dirname, '../test/fixtures')

// Load all PNG images in test/fixtures.
let files = fs.readdirSync(fixtures)
files = files.filter(function (f) { return f.endsWith('.png') })
// Specify the images in test/fixtures to use for benchmarking.
const files: string[] = [
'304x85.png'
]

// Create a benchmark for each image.
const benchmarks: any[] = []
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25 changes: 18 additions & 7 deletions src/index.ts
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Expand Up @@ -61,14 +61,25 @@ function measurePNG (header: Buffer): Result {
// detect returns the file format of the given header buffer. Format.UNKNOWN is
// returned if the file type is not supported.
function detect (header: Buffer): Format {
if (ascii(header, 1, 8) === 'PNG\r\n\x1a\n' && ascii(header, 12, 16) === 'IHDR') {
// PNG
if (
// _PNG\r\n\x1a\n
header[0] === 0x89 &&
header[1] === 0x50 &&
header[2] === 0x4e &&
header[3] === 0x47 &&
header[4] === 0x0d &&
header[5] === 0x0a &&
header[6] === 0x1a &&
header[7] === 0x0a &&
// IHDR
header[12] === 0x49 &&
header[13] === 0x48 &&
header[14] === 0x44 &&
header[15] === 0x52
) {
return Format.PNG
}
return Format.UNKNOWN
}

// ascii returns an ASCII string represented by the bytes in b from the start to
// end indexes.
function ascii (b: Buffer, start: number, end: number): string {
return b.toString('ascii', start, end)
return Format.UNKNOWN
}