fromInt64Bytes

Convert a signed 64-bit integer byte array to a double-precision floating-point number.

Installation

npm install @stdlib/number-float64-base-from-int64-bytes

Usage

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.

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.

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

Notes

• The function assumes host byte order (endianness).

Examples

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 );
}

See Also

• @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.

Notice

This package is part of 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, see the main project repository.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.