From 37a85dd4b7905fad4994fbf3312eaba4834b6b36 Mon Sep 17 00:00:00 2001 From: Branden Colen Date: Fri, 2 Apr 2021 23:27:08 -0500 Subject: [PATCH] improved runtime for converting from int --- README.md | 11 +++++------ romannumeral.go | 26 +++++++++++++++----------- romannumeral_test.go | 34 ++++++++++++++++------------------ 3 files changed, 36 insertions(+), 35 deletions(-) diff --git a/README.md b/README.md index fbe65f4..095741d 100644 --- a/README.md +++ b/README.md @@ -11,13 +11,12 @@ Quickly and efficiently convert to and from roman numerals in Go. goos: darwin goarch: arm64 pkg: github.com/brandenc40/romannumeral -BenchmarkIntToString-8 18160285 66.43 ns/op 24 B/op 2 allocs/op -BenchmarkIntToBytes-8 18630670 63.68 ns/op 24 B/op 2 allocs/op -BenchmarkStringToInt-8 17537406 67.26 ns/op 0 B/op 0 allocs/op -BenchmarkBytesToInt-8 18248730 64.83 ns/op 0 B/op 0 allocs/op +BenchmarkIntToString-8 56474846 20.84 ns/op 0 B/op 0 allocs/op +BenchmarkIntToBytes-8 48157634 24.36 ns/op 0 B/op 0 allocs/op +BenchmarkStringToInt-8 17584252 67.28 ns/op 0 B/op 0 allocs/op +BenchmarkBytesToInt-8 18343551 64.77 ns/op 0 B/op 0 allocs/op PASS -ok github.com/brandenc40/romannumeral 6.283s - +ok github.com/brandenc40/romannumeral 6.111s ``` ### Example diff --git a/romannumeral.go b/romannumeral.go index 7424238..09d2fd9 100644 --- a/romannumeral.go +++ b/romannumeral.go @@ -43,13 +43,22 @@ var _numerals = []numeral{ {1, []byte("I")}, } +// lookup arrays used for converting from an int to a roman numeral extremely quickly. +// inspired from https://rosettacode.org/wiki/Roman_numerals/Encode#Go +var ( + m0 = []string{"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"} + m1 = []string{"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"} + m2 = []string{"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"} + m3 = []string{"", "M", "MM", "MMM"} +) + // IntToString converts an integer value to a roman numeral string. An error is // returned if the integer is not between 1 and 3999. func IntToString(input int) (string, error) { if outOfBounds(input) { return "", IntegerOutOfBounds } - return string(intToRoman(input)), nil + return intToRoman(input), nil } // IntToBytes converts an integer value to a roman numeral byte array. An error is @@ -58,7 +67,7 @@ func IntToBytes(input int) ([]byte, error) { if outOfBounds(input) { return nil, IntegerOutOfBounds } - return intToRoman(input), nil + return []byte(intToRoman(input)), nil } // outOfBounds checks to ensure an input value is valid for roman numerals without the need of @@ -67,15 +76,10 @@ func outOfBounds(input int) bool { return input < _minRoman || input > _maxRoman } -func intToRoman(input int) []byte { - var output []byte - for _, rom := range _numerals { - for input >= rom.val { - output = append(output, rom.sym...) - input -= rom.val - } - } - return output +func intToRoman(n int) string { + // this is efficient in Go. the seven operands are evaluated, + // then a single allocation is made of the exact size needed for the result. + return m3[n%1e4/1e3] + m2[n%1e3/1e2] + m1[n%100/10] + m0[n%10] } // StringToInt converts a roman numeral string to an integer. Roman numerals for numbers diff --git a/romannumeral_test.go b/romannumeral_test.go index 2fd6b66..90d399f 100644 --- a/romannumeral_test.go +++ b/romannumeral_test.go @@ -6,24 +6,22 @@ import ( ) var testCases = map[string]int{ - "I": 1, "II": 2, - "III": 3, "IV": 4, - "V": 5, "VI": 6, - "VII": 7, "VIII": 8, - "IX": 9, "X": 10, - "XIV": 14, "XIX": 19, - "XX": 20, "XXXIII": 33, - "XXXIV": 34, "XXXIX": 39, - "XLIX": 49, "L": 50, - "LXXXIX": 89, "XCIX": 99, - "CXLIX": 149, "CCCXLIX": 349, - "CDLVI": 456, "D": 500, - "DCIV": 604, "DCCLXXXIX": 789, - "DCCCXLIX": 849, "CMIV": 904, - "MVII": 1007, "MLXVI": 1066, - "MDCCLXXVI": 1776, "MMDCCCVI": 2806, - "MMCMXCIX": 2999, "MMXXI": 2021, - "MMMCMLXXIX": 3979, "MMMCMXCIX": 3999, + "I": 1, "II": 2, "III": 3, "IV": 4, "V": 5, "VI": 6, + "VII": 7, "VIII": 8, "IX": 9, "X": 10, "XI": 11, "XII": 12, + "XIII": 13, "XIV": 14, "XV": 15, "XVI": 16, "XVII": 17, + "XVIII": 18, "XIX": 19, "XX": 20, "XXXI": 31, "XXXII": 32, + "XXXIII": 33, "XXXIV": 34, "XXXV": 35, "XXXVI": 36, "XXXVII": 37, + "XXXVIII": 38, "XXXIX": 39, "XL": 40, "XLI": 41, "XLII": 42, + "XLIII": 43, "XLIV": 44, "XLV": 45, "XLVI": 46, "XLVII": 47, + "XLVIII": 48, "XLIX": 49, "L": 50, "LXXXIX": 89, "XC": 90, + "XCI": 91, "XCII": 92, "XCIII": 93, "XCIV": 94, "XCV": 95, + "XCVI": 96, "XCVII": 97, "XCVIII": 98, "XCIX": 99, "C": 100, + "CI": 101, "CII": 102, "CIII": 103, "CIV": 104, "CV": 105, + "CVI": 106, "CVII": 107, "CVIII": 108, "CIX": 109, "CXLIX": 149, + "CCCXLIX": 349, "CDLVI": 456, "D": 500, "DCIV": 604, "DCCLXXXIX": 789, + "DCCCXLIX": 849, "CMIV": 904, "M": 1000, "MVII": 1007, "MLXVI": 1066, + "MCCXXXIV": 1234, "MDCCLXXVI": 1776, "MMXXI": 2021, "MMDCCCVI": 2806, + "MMCMXCIX": 2999, "MMM": 3000, "MMMCMLXXIX": 3979, "MMMCMXCIX": 3999, } func TestIntToString(t *testing.T) {