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fix: avoid premature overflow in math/base/special/cosh #16266

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fix: avoid premature overflow in math/base/special/cosh #16266

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7 changes: 7 additions & 0 deletions lib/node_modules/@stdlib/math/base/special/cosh/lib/main.js
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@

var isnan = require( '@stdlib/math/base/assert/is-nan' );
var exp = require( '@stdlib/math/base/special/exp' );
var MAX_LN = require( '@stdlib/constants/float64/max-ln' );


// MAIN //
Expand Down Expand Up @@ -78,13 +79,19 @@ var exp = require( '@stdlib/math/base/special/exp' );
* // returns NaN
*/
function cosh( x ) {
var t;
if ( isnan( x ) ) {
return x;
}
if ( x < 0.0 ) {
x = -x;
}
if ( x > 21.0 ) {
// Avoid premature overflow by evaluating `exp(x/2) * exp(x/2) / 2`:
if ( x > MAX_LN ) {
t = exp( 0.5 * x );
return ( 0.5 * t ) * t;
}
return exp( x ) / 2.0;
}
return ( exp(x) + exp(-x) ) / 2.0;
Expand Down
9 changes: 6 additions & 3 deletions lib/node_modules/@stdlib/math/base/special/cosh/manifest.json
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,8 @@
"dependencies": [
"@stdlib/math/base/napi/unary",
"@stdlib/math/base/assert/is-nan",
"@stdlib/math/base/special/exp"
"@stdlib/math/base/special/exp",
"@stdlib/constants/float64/max-ln"
]
},
{
Expand All @@ -53,7 +54,8 @@
"libpath": [],
"dependencies": [
"@stdlib/math/base/assert/is-nan",
"@stdlib/math/base/special/exp"
"@stdlib/math/base/special/exp",
"@stdlib/constants/float64/max-ln"
]
},
{
Expand All @@ -68,7 +70,8 @@
"libpath": [],
"dependencies": [
"@stdlib/math/base/assert/is-nan",
"@stdlib/math/base/special/exp"
"@stdlib/math/base/special/exp",
"@stdlib/constants/float64/max-ln"
]
}
]
Expand Down
7 changes: 7 additions & 0 deletions lib/node_modules/@stdlib/math/base/special/cosh/src/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@
#include "stdlib/math/base/special/cosh.h"
#include "stdlib/math/base/assert/is_nan.h"
#include "stdlib/math/base/special/exp.h"
#include "stdlib/constants/float64/max_ln.h"

/**
* Computes the hyperbolic cosine of a double-precision floating-point number.
Expand Down Expand Up @@ -61,6 +62,7 @@
*/
double stdlib_base_cosh( const double x ) {
double xc;
double t;
if ( stdlib_base_is_nan( x ) ) {
return x;
}
Expand All @@ -70,6 +72,11 @@ double stdlib_base_cosh( const double x ) {
xc = x;
}
if ( xc > 21.0 ) {
// Avoid premature overflow by evaluating `exp(x/2) * exp(x/2) / 2`:
if ( xc > STDLIB_CONSTANT_FLOAT64_MAX_LN ) {
t = stdlib_base_exp( 0.5 * xc );
return ( 0.5 * t ) * t;
}
return stdlib_base_exp( xc ) / 2.0;
}
return ( stdlib_base_exp( xc ) + stdlib_base_exp( -xc ) ) / 2.0;
Expand Down
22 changes: 22 additions & 0 deletions lib/node_modules/@stdlib/math/base/special/cosh/test/test.js
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Expand Up @@ -120,3 +120,25 @@ tape( 'the function returns `+infinity` if provided a `-infinity`', function tes
t.strictEqual( v, PINF, 'returns expected value' );
t.end();
});

tape( 'the function does not overflow for values whose hyperbolic cosine is representable', function test( t ) {
var expected;
var x;
var v;
var i;

x = [ 709.9, 710.0, 710.4 ];
expected = [
1.010701028059782e+308,
1.1169973830808555e+308,
1.6663642832806496e+308
];
for ( i = 0; i < x.length; i++ ) {
v = cosh( x[ i ] );
t.strictEqual( isAlmostSameValue( v, expected[ i ], 2 ), true, 'returns expected value' );
v = cosh( -x[ i ] );
t.strictEqual( isAlmostSameValue( v, expected[ i ], 2 ), true, 'returns expected value' );
}
t.strictEqual( cosh( 711.0 ), PINF, 'returns expected value' );
t.end();
});
22 changes: 22 additions & 0 deletions lib/node_modules/@stdlib/math/base/special/cosh/test/test.native.js
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Original file line number Diff line number Diff line change
Expand Up @@ -129,3 +129,25 @@ tape( 'the function returns `+infinity` if provided a `-infinity`', opts, functi
t.strictEqual( v, PINF, 'returns expected value' );
t.end();
});

tape( 'the function does not overflow for values whose hyperbolic cosine is representable', opts, function test( t ) {
var expected;
var x;
var v;
var i;

x = [ 709.9, 710.0, 710.4 ];
expected = [
1.010701028059782e+308,
1.1169973830808555e+308,
1.6663642832806496e+308
];
for ( i = 0; i < x.length; i++ ) {
v = cosh( x[ i ] );
t.strictEqual( isAlmostSameValue( v, expected[ i ], 2 ), true, 'returns expected value' );
v = cosh( -x[ i ] );
t.strictEqual( isAlmostSameValue( v, expected[ i ], 2 ), true, 'returns expected value' );
}
t.strictEqual( cosh( 711.0 ), PINF, 'returns expected value' );
t.end();
});
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