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manual.go
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manual.go
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// Copyright 2018 The CUE 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.
package math
import (
"math/big"
"github.com/cockroachdb/apd/v3"
"cuelang.org/go/internal"
)
func roundContext(rounder apd.Rounder) internal.Context {
c := internal.BaseContext
c.Rounding = rounder
return c
}
// TODO: for now we convert Decimals to int. This allows the desired type to be
// conveyed. This has the disadvantage that a number like 1E10000 will need to be
// expanded. Eventually it would be better to unify number types and allow
// anything that results in an integer to pose as an integer type.
// TODO: this is likely buggy, as we discard d.Exponent entirely.
func toInt(d *internal.Decimal) *big.Int {
i := &d.Coeff
if d.Negative {
i.Neg(i)
}
return i.MathBigInt()
}
// Floor returns the greatest integer value less than or equal to x.
//
// Special cases are:
//
// Floor(±0) = ±0
// Floor(±Inf) = ±Inf
// Floor(NaN) = NaN
func Floor(x *internal.Decimal) (*big.Int, error) {
var d internal.Decimal
_, err := internal.BaseContext.Floor(&d, x)
_, _ = internal.BaseContext.Quantize(&d, &d, 0)
return toInt(&d), err
}
// Ceil returns the least integer value greater than or equal to x.
//
// Special cases are:
//
// Ceil(±0) = ±0
// Ceil(±Inf) = ±Inf
// Ceil(NaN) = NaN
func Ceil(x *internal.Decimal) (*big.Int, error) {
var d internal.Decimal
_, err := internal.BaseContext.Ceil(&d, x)
_, _ = internal.BaseContext.Quantize(&d, &d, 0)
return toInt(&d), err
}
var roundTruncContext = roundContext(apd.RoundDown)
// Trunc returns the integer value of x.
//
// Special cases are:
//
// Trunc(±0) = ±0
// Trunc(±Inf) = ±Inf
// Trunc(NaN) = NaN
func Trunc(x *internal.Decimal) (*big.Int, error) {
var d internal.Decimal
_, err := roundTruncContext.RoundToIntegralExact(&d, x)
return toInt(&d), err
}
var roundUpContext = roundContext(apd.RoundHalfUp)
// Round returns the nearest integer, rounding half away from zero.
//
// Special cases are:
//
// Round(±0) = ±0
// Round(±Inf) = ±Inf
// Round(NaN) = NaN
func Round(x *internal.Decimal) (*big.Int, error) {
var d internal.Decimal
_, err := roundUpContext.RoundToIntegralExact(&d, x)
return toInt(&d), err
}
var roundEvenContext = roundContext(apd.RoundHalfEven)
// RoundToEven returns the nearest integer, rounding ties to even.
//
// Special cases are:
//
// RoundToEven(±0) = ±0
// RoundToEven(±Inf) = ±Inf
// RoundToEven(NaN) = NaN
func RoundToEven(x *internal.Decimal) (*big.Int, error) {
var d internal.Decimal
_, err := roundEvenContext.RoundToIntegralExact(&d, x)
return toInt(&d), err
}
var mulContext = internal.BaseContext.WithPrecision(1)
// MultipleOf reports whether x is a multiple of y.
func MultipleOf(x, y *internal.Decimal) (bool, error) {
var d apd.Decimal
cond, err := mulContext.Quo(&d, x, y)
return !cond.Inexact(), err
}