Convert a signed 64-bit integer byte array to a double-precision floating-point number.
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> Convert a signed 64-bit integer byte array to a [double-precision floating-point number][ieee754].
``bash`
npm install @stdlib/number-float64-base-from-int64-bytes
`javascript`
var fromInt64Bytes = require( '@stdlib/number-float64-base-from-int64-bytes' );
#### fromInt64Bytes( bytes, stride, offset )
Converts a signed 64-bit integer byte array to a [double-precision floating-point number][ieee754].
`javascript
var Uint8Array = require( '@stdlib/array-uint8' );
var bytes = new Uint8Array( [ 255, 255, 255, 255, 255, 255, 255, 255 ] );
var out = fromInt64Bytes( bytes, 1, 0 );
// returns -1.0
`
The function supports providing a stride and an index offset for indexing into a provided byte array.
`javascript
var Uint8Array = require( '@stdlib/array-uint8' );
var bytes = new Uint8Array( [ 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0, 255 ] );
var out = fromInt64Bytes( bytes, 2, 1 );
// returns -1.0
`
- The function assumes host byte order (endianness).
`javascript
var IS_LITTLE_ENDIAN = require( '@stdlib/assert-is-little-endian' );
var discreteUniform = require( '@stdlib/random-base-discrete-uniform' );
var bernoulli = require( '@stdlib/random-base-bernoulli' );
var Uint8Array = require( '@stdlib/array-uint8' );
var fromInt64Bytes = require( '@stdlib/number-float64-base-from-int64-bytes' );
var bytes;
var sgn;
var x;
var b;
var s;
var i;
var j;
var k;
bytes = new Uint8Array( 8 );
if ( IS_LITTLE_ENDIAN ) {
k = 0;
s = 1;
} else {
k = 7;
s = -1;
}
// Generate random integer-valued doubles on the interval (-2^16, 2^16)...
for ( i = 0; i < 10; i++ ) {
// Determine the sign:
sgn = ( bernoulli( 0.5 ) ) ? 0 : 128; // 2^7
// Set a subset of individual (lower-order) bytes:
for ( j = 0; j < 2; j++ ) {
b = discreteUniform( 0, 255 ); // 2^8-1
bytes[ k+(j*s) ] = b;
}
// Set higher-order bytes using two's complement:
for ( j = 2; j < 8; j++ ) {
bytes[ k+(j*s) ] = ( sgn ) ? 255 : 0; // 2^8-1
}
// Convert the bytes to a double:
x = fromInt64Bytes( bytes, 1, 0 );
console.log( bytes + ' => ' + x );
}
`
*
- [@stdlib/number-float64/base/to-int64-bytes][@stdlib/number/float64/base/to-int64-bytes]: convert an integer-valued double-precision floating-point number to a signed 64-bit integer byte array according to host byte order.
*
This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].
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---
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[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985
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