KumaChan/standalone/util/numeric.go

package util

import (
	"math"
	"math/big"
	"math/cmplx"
	"strconv"
	"unicode"
	"unicode/utf8"
)


const MaxSafeIntegerToDouble = 9007199254740991
const MinSafeIntegerToDouble = -9007199254740991

func GetNumberUint(small uint) *big.Int {
	var n big.Int
	n.SetUint64(uint64(small))
	return &n
}

func GetNumberUint64(small uint64) *big.Int {
	var n big.Int
	n.SetUint64(small)
	return &n
}

func GetUintNumber(n *big.Int) uint {
	if n.Cmp(big.NewInt(0)) < 0 { panic("something went wrong") }
	var limit big.Int
	limit.SetUint64(uint64(^uint(0)))
	if n.Cmp(&limit) <= 0 {
		return uint(n.Uint64())
	} else {
		panic("given number too big")
	}
}

func GetInt64Integer(n *big.Int) int64 {
	if n.IsInt64() {
		return n.Int64()
	} else {
		panic("given number too big")
	}
}

func IsNonNegative(n *big.Int) bool {
	return (n.Cmp(big.NewInt(0)) >= 0)
}

func IsNormalFloat(x float64) bool {
	return !(math.IsNaN(x) || math.IsInf(x, 0))
}

func IsNormalComplex(z complex128) bool {
	return !(cmplx.IsNaN(z) || cmplx.IsInf(z))
}

func WellBehavedParseInteger(chars ([] rune)) (*big.Int, bool) {
	var abs_chars ([] rune)
	if chars[0] == '-' {
		abs_chars = chars[1:]
	} else {
		abs_chars = chars
	}
	var has_base_prefix = false
	if len(abs_chars) >= 2 {
		var c1 = abs_chars[0]
		var c2 = abs_chars[1]
		if c1 == '0' &&
		(c2 == 'x' || c2 == 'o' || c2 == 'b' ||
		c2 == 'X' || c2 == 'O' || c2 == 'B') {
			has_base_prefix = true
		}
	}
	var str = string(chars)
	// note: forbid "0" as octal prefix
	if has_base_prefix {
		return big.NewInt(0).SetString(str, 0)
	} else {
		if len(str) >= 2 && str[0] == '0' {
			return nil, false
		}
		return big.NewInt(0).SetString(str, 10)
	}
}

func IntegerToDouble(value *big.Int) (float64, bool) {
	if value.IsInt64() {
		var i64 = value.Int64()
		var ok = MinSafeIntegerToDouble <= i64 && i64 <= MaxSafeIntegerToDouble
		if ok {
			return float64(i64), true
		} else {
			return math.NaN(), false
		}
	} else {
		return math.NaN(), false
	}
}

func ParseDouble(chars ([] rune)) (float64, bool) {
	var value, err = strconv.ParseFloat(string(chars), 64)
	if err != nil { return math.NaN(), false }
	return value, true
}

func ParseRune(chars ([] rune)) (rune, bool) {
	const E = utf8.RuneError
	var invalid = func() (rune, bool) {
		return E, false
	}
	var got = func(r rune) (rune, bool) {
		return r, true
	}
	if len(chars) == 0 {
		return invalid()
	} else if len(chars) == 1 {
		return got(chars[0])
	} else {
		var c0 = chars[0]
		if c0 == '`' {
			return got(chars[1])
		} else if c0 == '\\' {
			var c1 = chars[1]
			switch c1 {
			case 'n':
				return got('\n')
			case 'r':
				return got('\r')
			case 't':
				return got('\t')
			case 'e':
				return got('\033')
			case 'b':
				return got('\b')
			case 'a':
				return got('\a')
			case 'f':
				return got('\f')
			case 'u':
				var code_point_raw = string(chars[2:])
				var n, ok1 = big.NewInt(0).SetString(code_point_raw, 16)
				if !ok1 { return invalid() }
				var min = big.NewInt(0)
				var max = big.NewInt(unicode.MaxRune)
				var ok2 = ((min.Cmp(n) <= 0) && (n.Cmp(max) <= 0))
				if !ok2 { return invalid() }
				return got(rune(n.Int64()))
			default:
				return invalid()
			}
		} else {
			return invalid()
		}
	}
}