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LibJS: Unify exponentiation logic for ** operator and Math.pow

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The JS behaviour of exponentiation on two number typed values is
not a simple matter of forwarding to ::pow(double, double). So,
this factors out the Math.pow logic to allow it to be shared with
Value::exp.
This commit is contained in:
Anonymous 2022-02-17 11:52:45 -08:00 committed by Linus Groh
parent c0735b047e
commit c45922c637
Notes: sideshowbarker 2024-07-19 18:29:38 +09:00 
Committer: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/c45922c6379
3 changed files with 70 additions and 48 deletions
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48
Userland/Libraries/LibJS/Runtime/MathObject.cpp
View File

@ -216,53 +216,7 @@ JS_DEFINE_NATIVE_FUNCTION(MathObject::pow)
{
auto base = TRY(vm.argument(0).to_number(global_object));
auto exponent = TRY(vm.argument(1).to_number(global_object));
if (exponent.is_nan())
return js_nan();
if (exponent.is_positive_zero() || exponent.is_negative_zero())
return Value(1);
if (base.is_nan())
return js_nan();
if (base.is_positive_infinity())
return exponent.as_double() > 0 ? js_infinity() : Value(0);
if (base.is_negative_infinity()) {
auto is_odd_integral_number = exponent.is_integral_number() && (exponent.as_i32() % 2 != 0);
if (exponent.as_double() > 0)
return is_odd_integral_number ? js_negative_infinity() : js_infinity();
else
return is_odd_integral_number ? Value(-0.0) : Value(0);
}
if (base.is_positive_zero())
return exponent.as_double() > 0 ? Value(0) : js_infinity();
if (base.is_negative_zero()) {
auto is_odd_integral_number = exponent.is_integral_number() && (exponent.as_i32() % 2 != 0);
if (exponent.as_double() > 0)
return is_odd_integral_number ? Value(-0.0) : Value(0);
else
return is_odd_integral_number ? js_negative_infinity() : js_infinity();
}
VERIFY(base.is_finite_number() && !base.is_positive_zero() && !base.is_negative_zero());
if (exponent.is_positive_infinity()) {
auto absolute_base = fabs(base.as_double());
if (absolute_base > 1)
return js_infinity();
else if (absolute_base == 1)
return js_nan();
else if (absolute_base < 1)
return Value(0);
}
if (exponent.is_negative_infinity()) {
auto absolute_base = fabs(base.as_double());
if (absolute_base > 1)
return Value(0);
else if (absolute_base == 1)
return js_nan();
else if (absolute_base < 1)
return js_infinity();
}
VERIFY(exponent.is_finite_number() && !exponent.is_positive_zero() && !exponent.is_negative_zero());
if (base.as_double() < 0 && !exponent.is_integral_number())
return js_nan();
return Value(::pow(base.as_double(), exponent.as_double()));
return JS::exp(global_object, base, exponent);
}
// 21.3.2.14 Math.exp ( x ), https://tc39.es/ecma262/#sec-math.exp

55
Userland/Libraries/LibJS/Runtime/Value.cpp
View File

@ -6,6 +6,7 @@
*/
#include <AK/AllOf.h>
#include <AK/Assertions.h>
#include <AK/CharacterTypes.h>
#include <AK/String.h>
#include <AK/StringBuilder.h>
@ -1192,6 +1193,58 @@ ThrowCompletionOr<Value> mod(GlobalObject& global_object, Value lhs, Value rhs)
return vm.throw_completion<TypeError>(global_object, ErrorType::BigIntBadOperatorOtherType, "modulo");
}
static Value exp_double(Value base, Value exponent)
{
VERIFY(both_number(base, exponent));
if (exponent.is_nan())
return js_nan();
if (exponent.is_positive_zero() || exponent.is_negative_zero())
return Value(1);
if (base.is_nan())
return js_nan();
if (base.is_positive_infinity())
return exponent.as_double() > 0 ? js_infinity() : Value(0);
if (base.is_negative_infinity()) {
auto is_odd_integral_number = exponent.is_integral_number() && (exponent.as_i32() % 2 != 0);
if (exponent.as_double() > 0)
return is_odd_integral_number ? js_negative_infinity() : js_infinity();
else
return is_odd_integral_number ? Value(-0.0) : Value(0);
}
if (base.is_positive_zero())
return exponent.as_double() > 0 ? Value(0) : js_infinity();
if (base.is_negative_zero()) {
auto is_odd_integral_number = exponent.is_integral_number() && (exponent.as_i32() % 2 != 0);
if (exponent.as_double() > 0)
return is_odd_integral_number ? Value(-0.0) : Value(0);
else
return is_odd_integral_number ? js_negative_infinity() : js_infinity();
}
VERIFY(base.is_finite_number() && !base.is_positive_zero() && !base.is_negative_zero());
if (exponent.is_positive_infinity()) {
auto absolute_base = fabs(base.as_double());
if (absolute_base > 1)
return js_infinity();
else if (absolute_base == 1)
return js_nan();
else if (absolute_base < 1)
return Value(0);
}
if (exponent.is_negative_infinity()) {
auto absolute_base = fabs(base.as_double());
if (absolute_base > 1)
return Value(0);
else if (absolute_base == 1)
return js_nan();
else if (absolute_base < 1)
return js_infinity();
}
VERIFY(exponent.is_finite_number() && !exponent.is_positive_zero() && !exponent.is_negative_zero());
if (base.as_double() < 0 && !exponent.is_integral_number())
return js_nan();
return Value(::pow(base.as_double(), exponent.as_double()));
}
// 13.6 Exponentiation Operator, https://tc39.es/ecma262/#sec-exp-operator
ThrowCompletionOr<Value> exp(GlobalObject& global_object, Value lhs, Value rhs)
{
@ -1199,7 +1252,7 @@ ThrowCompletionOr<Value> exp(GlobalObject& global_object, Value lhs, Value rhs)
auto lhs_numeric = TRY(lhs.to_numeric(global_object));
auto rhs_numeric = TRY(rhs.to_numeric(global_object));
if (both_number(lhs_numeric, rhs_numeric))
return Value(pow(lhs_numeric.as_double(), rhs_numeric.as_double()));
return exp_double(lhs_numeric, rhs_numeric);
if (both_bigint(lhs_numeric, rhs_numeric)) {
if (rhs_numeric.as_bigint().big_integer().is_negative())
return vm.throw_completion<RangeError>(global_object, ErrorType::NegativeExponent);

15
Userland/Libraries/LibJS/Tests/exponentiation-basic.js
View File

@ -35,3 +35,18 @@ test("exponentiation that produces NaN", () => {
expect(2 ** "foo").toBeNaN();
expect("foo" ** 2).toBeNaN();
});
test("exponentiation with infinities", () => {
expect((-1) ** Infinity).toBeNaN();
expect(0 ** Infinity).toBe(0);
expect(1 ** Infinity).toBeNaN();
expect((-1) ** -Infinity).toBeNaN();
expect(0 ** -Infinity).toBe(Infinity);
expect(1 ** -Infinity).toBeNaN();
expect(Infinity ** -1).toBe(0);
expect(Infinity ** 0).toBe(1);
expect(Infinity ** 1).toBe(Infinity);
expect((-Infinity) ** -1).toBe(-0);
expect((-Infinity) ** 0).toBe(1);
expect((-Infinity) ** 1).toBe(-Infinity);
});