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* @license Apache-2.0
*
* Copyright (c) 2026 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var isInfinitef = require( '@stdlib/math/base/assert/is-infinitef' );
var isnanf = require( '@stdlib/math/base/assert/is-nanf' );
var exponentf = require( '@stdlib/number/float32/base/exponent' );
var f32 = require( '@stdlib/number/float64/base/to-float32' );
var log10f = require( '@stdlib/math/base/special/log10f' );
var floorf = require( '@stdlib/math/base/special/floorf' );
var truncf = require( '@stdlib/math/base/special/truncf' );
var powf = require( '@stdlib/math/base/special/powf' );
var absf = require( '@stdlib/math/base/special/absf' );
var lnf = require( '@stdlib/math/base/special/lnf' );
// MAIN //
/**
* Rounds a single-precision floating-point number to the nearest number toward zero with `n` significant figures.
*
* @param {number} x - input value
* @param {PositiveInteger} n - number of significant figures
* @param {PositiveInteger} b - base
* @returns {number} rounded value
*
* @example
* var v = truncsdf( 3.1415927410125732, 5, 10 );
* // returns 3.1414999961853027
*
* @example
* var v = truncsdf( 3.1415927410125732, 1, 10 );
* // returns 3.0
*
* @example
* var v = truncsdf( 12368.0, 2, 10 );
* // returns 12000.0
*
* @example
* var v = truncsdf( 0.0313, 2, 2 );
* // returns 0.03125
*/
function truncsdf( x, n, b ) {
var exp;
var s;
var y;
x = f32( x );
if (
isnanf( x ) ||
isnanf( n ) ||
n < 1 ||
isInfinitef( n ) ||
isnanf( b ) ||
b <= 0 ||
isInfinitef( b )
) {
return NaN;
}
if ( isInfinitef( x ) || x === 0.0 ) {
return x;
}
if ( b === 10 ) {
exp = log10f( absf( x ) );
} else if ( b === 2 ) {
exp = exponentf( absf( x ) );
} else {
exp = f32( lnf( absf( x ) ) / lnf( f32( b ) ) );
}
exp = floorf( f32( f32( exp - f32( n ) ) + 1.0 ) );
s = powf( f32( b ), absf( exp ) );
// Check for overflow:
if ( isInfinitef( s ) ) {
return x;
}
// To avoid numerical stability issues due to floating-point rounding error, we must treat positive and negative exponents separately:
if ( exp < 0.0 ) {
y = f32( truncf( f32( x * s ) ) / s );
} else {
y = f32( truncf( f32( x / s ) ) * s );
}
// Check for overflow:
if ( isInfinitef( y ) ) {
return x;
}
return y;
}
// EXPORTS //
module.exports = truncsdf;
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