roundn

Round a double-precision floating-point number to the nearest multiple of 10^n.

Usage

var roundn = require( '@stdlib/math/base/special/roundn' );

roundn( x, n )

Rounds a double-precision floating-point number to the nearest multiple of 10^n.

// Round a value to 2 decimal places:
var v = roundn( 3.141592653589793, -2 );
// returns 3.14

// If n = 0, `roundn` behaves like `round`:
v = roundn( 3.141592653589793, 0 );
// returns 3.0

// Round a value to the nearest thousand:
v = roundn( 12368.0, 3 );
// returns 12000.0

Notes

When operating on floating-point numbers in bases other than 2, rounding to specified digits can be inexact. For example,

var x = 0.2 + 0.1;
// returns 0.30000000000000004

// Should round to 0.3...
var v = roundn( x, -16 );
// returns 0.3000000000000001

Examples

var randu = require( '@stdlib/random/base/randu' );
var roundn = require( '@stdlib/math/base/special/roundn' );

var x;
var n;
var v;
var i;

for ( i = 0; i < 100; i++ ) {
    x = (randu()*100.0) - 50.0;
    n = roundn( randu()*5.0, 0 );
    v = roundn( x, -n );
    console.log( 'x: %d. Number of decimals: %d. Rounded: %d.', x, n, v );
}

C APIs

Usage

#include "stdlib/math/base/special/roundn.h"

stdlib_base_roundn( x, n )

Rounds a double-precision floating-point number to the nearest multiple of 10^n.

double y = stdlib_base_roundn( 3.14, -2 );
// returns 3.14

The function accepts the following arguments:

x: [in] double input value.
n: [in] int32_t integer power of 10.

double stdlib_base_roundn( const double x, const int32_t n );

Examples

#include "stdlib/math/base/special/roundn.h"
#include <stdio.h>

int main( void ) {
    const double x[] = { 3.14, -3.14, 0.0, 0.0/0.0 };

    double y;
    int i;
    for ( i = 0; i < 4; i++ ) {
        y = stdlib_base_roundn( x[ i ], -2 );
        printf( "roundn(%lf) = %lf\n", x[ i ], y );
    }
}