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@nvictus nvictus/loadnpy.js
Last active Apr 25, 2019

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NumPy binary file parser for javascript
// Client-side parser for .npy files
// See the specification: http://docs.scipy.org/doc/numpy-dev/neps/npy-format.html
var NumpyLoader = (function () {
function asciiDecode(buf) {
return String.fromCharCode.apply(null, new Uint8Array(buf));
}
function readUint16LE(buffer) {
var view = new DataView(buffer);
var val = view.getUint8(0);
val |= view.getUint8(1) << 8;
return val;
}
function fromArrayBuffer(buf) {
// Check the magic number
var magic = asciiDecode(buf.slice(0,6));
if (magic.slice(1,6) != 'NUMPY') {
throw new Error('unknown file type');
}
var version = new Uint8Array(buf.slice(6,8)),
headerLength = readUint16LE(buf.slice(8,10)),
headerStr = asciiDecode(buf.slice(10, 10+headerLength));
offsetBytes = 10 + headerLength;
//rest = buf.slice(10+headerLength); XXX -- This makes a copy!!! https://www.khronos.org/registry/typedarray/specs/latest/#5
// Hacky conversion of dict literal string to JS Object
eval("var info = " + headerStr.toLowerCase().replace('(','[').replace('),',']'));
// Intepret the bytes according to the specified dtype
var data;
if (info.descr === "|u1") {
data = new Uint8Array(buf, offsetBytes);
} else if (info.descr === "|i1") {
data = new Int8Array(buf, offsetBytes);
} else if (info.descr === "<u2") {
data = new Uint16Array(buf, offsetBytes);
} else if (info.descr === "<i2") {
data = new Int16Array(buf, offsetBytes);
} else if (info.descr === "<u4") {
data = new Uint32Array(buf, offsetBytes);
} else if (info.descr === "<i4") {
data = new Int32Array(buf, offsetBytes);
} else if (info.descr === "<f4") {
data = new Float32Array(buf, offsetBytes);
} else if (info.descr === "<f8") {
data = new Float64Array(buf, offsetBytes);
} else {
throw new Error('unknown numeric dtype')
}
return {
shape: info.shape,
fortran_order: info.fortran_order,
data: data
};
}
function open(file, callback) {
var reader = new FileReader();
reader.onload = function() {
// the file contents have been read as an array buffer
var buf = reader.result;
var ndarray = fromArrayBuffer(buf);
callback(ndarray);
};
reader.readAsArrayBuffer(file);
}
function ajax(url, callback) {
var xhr = new XMLHttpRequest();
xhr.onload = function(e) {
var buf = xhr.response; // not responseText
var ndarray = fromArrayBuffer(buf);
callback(ndarray);
};
xhr.open("GET", url, true);
xhr.responseType = "arraybuffer";
xhr.send(null);
}
return {
open: open,
ajax: ajax
};
})();
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