Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
数値を文字列に整形する際の落とし穴とその解決策(iOSDC2024 ルーキーズLT) / iO...
Search
glassfiber
August 23, 2024
Programming
0
720
数値を文字列に整形する際の落とし穴とその解決策(iOSDC2024 ルーキーズLT) / iOSDC Japan 2024 Formatting Floating-Point Numbers
数値を文字列に整形する際に陥った落とし穴について、具体例を交えて紹介します。
glassfiber
August 23, 2024
Tweet
Share
More Decks by glassfiber
See All by glassfiber
pixiv App Night 20240523 NumberFormatterのハマり事例
glassfiber
0
170
Other Decks in Programming
See All in Programming
ソフトウェアテスト徹底指南書の紹介
goyoki
1
110
The state patternの実践 個人開発で培ったpractice集
miyanokomiya
0
150
あのころの iPod を どうにか再生させたい
orumin
2
2.5k
🔨 小さなビルドシステムを作る
momeemt
2
530
[FEConf 2025] 모노레포 절망편, 14개 레포로 부활하기까지 걸린 1년
mmmaxkim
0
1.1k
UbieのAIパートナーを支えるコンテキストエンジニアリング実践
syucream
2
730
実践!App Intents対応
yuukiw00w
1
350
Rancher と Terraform
fufuhu
0
110
オープンセミナー2025@広島「君はどこで動かすか?」アンケート結果
satoshi256kbyte
0
210
デザインシステムが必須の時代に
yosuke_furukawa
PRO
2
110
開発チーム・開発組織の設計改善スキルの向上
masuda220
PRO
15
8.1k
マイコンでもRustのtestがしたい その2/KernelVM Tokyo 18
tnishinaga
2
2.3k
Featured
See All Featured
The Web Performance Landscape in 2024 [PerfNow 2024]
tammyeverts
9
780
GraphQLとの向き合い方2022年版
quramy
49
14k
Exploring the Power of Turbo Streams & Action Cable | RailsConf2023
kevinliebholz
34
6k
Learning to Love Humans: Emotional Interface Design
aarron
273
40k
Fireside Chat
paigeccino
39
3.6k
Designing Experiences People Love
moore
142
24k
I Don’t Have Time: Getting Over the Fear to Launch Your Podcast
jcasabona
33
2.4k
Save Time (by Creating Custom Rails Generators)
garrettdimon
PRO
32
1.4k
How STYLIGHT went responsive
nonsquared
100
5.7k
The Success of Rails: Ensuring Growth for the Next 100 Years
eileencodes
46
7.6k
Agile that works and the tools we love
rasmusluckow
329
21k
CoffeeScript is Beautiful & I Never Want to Write Plain JavaScript Again
sstephenson
161
15k
Transcript
glass fi ber (ϐΫγϒגࣜձࣾʣ Λจࣈྻʹܗ͢Δࡍͷ མͱ݀͠ͱͦͷղܾࡦ iOSDC Japan 2024 2024/08/23
Track A ϧʔΩʔζLT
00 iOS։ൃʹ6ϒϥϯΫͷ͋Δ ΤϯδχΞ͕෮ؼͨ͠Β ͷܗͰͲϋϚΓͨ͠
༻Λύʔηϯτදࣔ͢Δ • ετϨʔδͷ༻Λύʔηϯτදࣔ • ཁ: ͋Μ·Γͯ͘ݟʹ͍͘ͷͰ͍͍ײ͡ͷܻͰग़ͯ͠ཉ͍͠ (খୈ2Ґ͘Β͍ʁ) 00 ←͜Μͳײ͡ͷͭ
༻Λύʔηϯτදࣔ͢Δ • খୈ2Ґ·Ͱදࣔ͢ΔίʔυΛॻ͖·ͨ͠ • ҰݟΑͦ͞͏ʹݟ͑·͢ ͕ 00 let usageRate =
0.12345 let value = round(usageRate * 10000) / 10000 let percentValue = value * 100 print("\(percentValue)%") 12.35% ↑0.01%=0.0001ͳͷͰ ɹখୈ5ҐͰ࢛ࣺޒೖ͢Δ
• ʹΑͬͯظ͢ΔදࣔʹͳΒͳ͍͜ͱ͕໌ • ͨͱ͕͑0.523ͷͱ͖ • খҎԼͷܻ͕ͱͯ͘ͳͬͯ͠·͏ 52.300000000000004% ʮͳΜ͔ද͕͓͔ࣔ͘͠ͳΔʯͱ͍͏ใࠂ͕ 00 let
usageRate = 0.523 let value = round(usageRate * 10000) / 10000 let percentValue = value * 100 print("\(percentValue)%")
ͳΜͰ͜͏ͳΔͷ͔ • ුಈখͷޡ͕ࠩӨڹ • 2ਐͰදݱͰ͖ͳ͍ޡؚ͕ࠩ·ΕΔ • ࢛ࣺޒೖͨͣ͠ͳͷʹɺ100ഒͨ͠Β·ͨԼҐͷܻ͕ݱΕΔ… • ͱΓ͋͑ͣɺύʔηϯτද͍ࣔͨ͠ͱ͖ʹ100ഒͯ͠ͳΜͱ͔͠Α͏ͱ ͢ΔͷΑ͘ͳͦ͞͏
00
ܻΛࢦఆͨ͠ΒΑ͍ͷͰ • String(format:)ͰখҎԼͷܻΛࢦఆͨ͠ΒͲ͏Ͱ͠ΐ͏ • ݁Ռɺܻ͕ݻఆͳͷͰɺඌʹ0͕ͭ͘ • ͜ΕͰ͍͍͕ɺ͏ͪΐͬͱ͍͍ײ͡ʹ͍ͨ͠ • ඌͷ0ͳ͍ͨ͘͠ 00
let usageRate = 0.523 let value = round(usageRate * 10000) / 10000 print("\(String(format: "%.2f", value * 100))%") 52.30% ↑খҎԼ2ܻ
ͷܗͱ͍͑NumberFormatter • numberStyle = .percent ͱ͢Ε100ഒͤͣͱύʔηϯτදهʹͳΔ • ͢Β͍͠ 00 let
usageRate = 0.523 let formatter = NumberFormatter() formatter.numberStyle = .percent formatter.maximumFractionDigits = 2 if let str = formatter.string(from: NSNumber(value: usageRate)) { print(str) } 52.3% ←খҎԼ࠷େ2ܻ
খҎԼ2ܻʹͰ͖ͨɺ͚Ͳ • ཁ͕͖ͨ • 12.34%ͱ͍͏ͷ͍ɺͰे • Ͱ0.12%͜ͷ··খҎԼ2ܻग़ͯཉ͍͠ • →ʹΑܻͬͯΛ͍͍ײ͡ʹΓସ͍͑ͨ 00
let formatter = NumberFormatter() formatter.numberStyle = .percent func myFormat(_ value: Double) -> String { formatter.maximumFractionDigits = 2 return formatter.string(from: NSNumber(value: value)) ?? "" } print(myFormat(0.12345)) print(myFormat(0.012345)) print(myFormat(0.0012345)) 12.34% 1.23% 0.12%
ͰɺܻΛΓସ͑ͯΈΔ 00 let formatter = NumberFormatter() formatter.numberStyle = .percent func
myFormat(_ value: Double) -> String { formatter.maximumFractionDigits = switch value { case ..<1: 2 case ..<10: 1 default: 0 } return formatter.string(from: NSNumber(value: value)) ?? "" } print(myFormat(0.12345)) print(myFormat(0.012345)) print(myFormat(0.0012345)) ←ͷൣғͰ߹͚ܻͯ͠ΛΓସ͑Δ 1%ະຬ / 1%Ҏ্10%ະຬ / 10%Ҏ্
ͰɺܻΛΓସ͑ͯΈΔ 00 let formatter = NumberFormatter() formatter.numberStyle = .percent func
myFormat(_ value: Double) -> String { formatter.maximumFractionDigits = switch value { case ..<1: 2 case ..<10: 1 default: 0 } return formatter.string(from: NSNumber(value: value)) ?? "" } print(myFormat(0.12345)) print(myFormat(0.012345)) print(myFormat(0.0012345)) ←ͷൣғͰ߹͚ܻͯ͠ΛΓସ͑Δ 1%ະຬ / 1%Ҏ্10%ະຬ / 10%Ҏ্ 12.34% 1.23% 0.12% มΘͬͯͳ͍…ʁ
ͰɺܻΛΓସ͑ͯΈΔ 00 let formatter = NumberFormatter() formatter.numberStyle = .percent func
myFormat(_ value: Double) -> String { formatter.maximumFractionDigits = switch value { case ..<1: 2 case ..<10: 1 default: 0 } return formatter.string(from: NSNumber(value: value)) ?? "" } print(myFormat(0.12345)) print(myFormat(0.012345)) print(myFormat(0.0012345)) 12.34% 1.23% 0.12% มΘͬͯͳ͍…ʁ ←ˋͷͰൺֱ͢Δؒҧ͍ (Α͘Δ)
ͰɺܻΛΓସ͑ͯΈΔ 00 let formatter = NumberFormatter() formatter.numberStyle = .percent func
myFormat(_ value: Double) -> String { formatter.maximumFractionDigits = switch value { case ..<0.01: 2 case ..<0.1: 1 default: 0 } return formatter.string(from: NSNumber(value: value)) ?? "" } print(myFormat(0.12345)) print(myFormat(0.012345)) print(myFormat(0.0012345)) ←ͷൣғͰ߹͚ܻͯ͠ΛΓସ͑Δ 1%ະຬ / 1%Ҏ্10%ະຬ / 10%Ҏ্
ͰɺܻΛΓସ͑ͯΈΔ 00 let formatter = NumberFormatter() formatter.numberStyle = .percent func
myFormat(_ value: Double) -> String { formatter.maximumFractionDigits = switch value { case ..<0.01: 2 case ..<0.1: 1 default: 0 } return formatter.string(from: NSNumber(value: value)) ?? "" } print(myFormat(0.12345)) print(myFormat(0.012345)) print(myFormat(0.0012345)) 12% 1.2% 0.12% ͍͍ײ͡ ←ͷൣғͰ߹͚ܻͯ͠ΛΓସ͑Δ 1%ະຬ / 1%Ҏ্10%ະຬ / 10%Ҏ্
ද͍͍ࣔײ͚ͩ͡Ͳɺίʔυ͕ؾʹೖΒͳ͍ • switchͰ͚ΔͷͳΜ͔ΠϚΠν 00 formatter.maximumFractionDigits = switch value { case
..<0.01: 2 case ..<0.1: 1 default: 0 }
Ͳ͏͍ͨ͠ͷ͔ߟ͑ͯΈΔ • ༗ޮࣈ͕2ܻɺͱ͍͏͜ͱͰΑͦ͞͏…ʁ • NumberFomatterʹ༗ޮܻΛࢦఆ͢Δػೳ͕͋Δ (maximumSigni fi cantDigits) 00 →
→ → 12% 1.2% 0.12% 0.12345 0.012345 0.0012345 ͜ͷͷͱ͖ ͜͏͍ͨ͠
༗ޮࣈ2ܻͰܗ͢Δ 00 let formatter = NumberFormatter() formatter.numberStyle = .percent formatter.usesSignificantDigits
= true formatter.maximumSignificantDigits = 2 func myFormat(_ value: Double) -> String { return formatter.string(from: NSNumber(value: value)) ?? "" } print(myFormat(0.12345)) print(myFormat(0.012345)) print(myFormat(0.0012345)) 12% 1.2% 0.12% ←༗ޮܻ2ܻʹઃఆ Αͦ͞͏…ʁ
খ͍͞ͷͱ͖ʹ͘ͳͬͯ͠·͏ͱࢦఠ͞ΕΔ 00 let formatter = NumberFormatter() formatter.numberStyle = .percent formatter.usesSignificantDigits
= true formatter.maximumSignificantDigits = 2 func myFormat(_ value: Double) -> String { return formatter.string(from: NSNumber(value: value)) ?? "" } print(myFormat(0.12345)) print(myFormat(0.012345)) print(myFormat(0.0012345)) print(myFormat(0.00012345)) print(myFormat(0.00000012345)) 12% 1.2% 0.12% 0.012% 0.000012%
খ͍͞ͷͱ͖ʹ͘ͳͬͯ͠·͏ • খ͍͞ͷͱ͖ʹ͔ͬ͠Γ༗ޮࣈ2ܻͰग़ΔͷͰ͘ͳΔ • খ෦ͷܻࢦఆ(maximumFractionDigits) จࣈྻͷ੍͕͞ݶ͞ ΕΔ͕ɺ༗ޮܻࢦఆ(maximumSigni fi cantDigits) ͦ͏Ͱͳ͍
• ͦΕͦ͏ 00 print(myFormat(0.00012345)) print(myFormat(0.00000012345)) 0.012% 0.000012%
খ͍ܻ͞Λ࢛ࣺޒೖͯ͠ղܾ • ࠷ॳʹ͍ͬͯͨɺখୈ5ҐͰͷ࢛ࣺޒೖΛ࠶ͼಋೖ͠·͢ • Α͏͍͍͘ײ͡ʹͰ͖·ͨ͠ 00 func myFormat(_ value: Double)
-> String { let roundedValue = round(value * 10000) / 10000 return formatter.string(from: NSNumber(value: roundedValue)) ?? "" } print(myFormat(0.12345)) print(myFormat(0.012345)) print(myFormat(0.0012345)) print(myFormat(0.00012345)) print(myFormat(0.00000012345)) ←খୈ5ҐͰ࢛ࣺޒೖ 12% 1.2% 0.12% 0.01% 0%
func test_༻༰ྔ͕0ͷͱ͖ʹ0ύʔηϯτදهʹͳΔ() { let usage = 0 let limit =
1000000 * 1000 * 1000 let user = testUser(usage, limit) XCTAssertEqual(user.storageUsageFormatted, "0%") } func test_༻༰ྔ͕0_01ύʔηϯτະຬͷͱ͖ʹ0ύʔηϯτදهʹͳΔ let usage = 12 * 1000 * 1000 let limit = 1000000 * 1000 * 1000 let user = testUser(usage, limit) XCTAssertEqual(user.storageUsageFormatted, "0%") } func test_༻༰ྔ͕0_1ύʔηϯτະຬͷͱ͖ʹখ2Ґ·ͰͷදهʹͳΔ let usage = 123 * 1000 * 1000 let limit = 1000000 * 1000 * 1000 let user = testUser(usage, limit) XCTAssertEqual(user.storageUsageFormatted, "0.01%") } func test_༻༰ྔ͕1ύʔηϯτະຬͷͱ͖ʹখ2Ґ·ͰͷදهʹͳΔ() let usage = 1234 * 1000 * 1000 let limit = 1000000 * 1000 * 1000 let user = testUser(usage, limit) XCTAssertEqual(user.storageUsageFormatted, "0.12%") } func test_༻༰ྔ͕10ύʔηϯτະຬͷͱ͖ʹখ1Ґ·ͰͷදهʹͳΔ( ςετΛॻ͍ͯ҆৺͢Δ • Ͳ͏ͳͬͯ΄͍͔͠ΛͪΌ Μͱॻ͍ͯ֬ೝ͢Δ • ࣮ࡍͷετϨʔδ༰ྔͰද ࣔΛ֬ೝ͢Δͷඇݱ࣮త • ϋϚΔͳͲΛཏྻ͠ ͯɺظ͢ΔදࣔʹͳΔ͜ ͱΛ֬ೝ
·ͱΊ • ුಈখͷѻ͍͍͠ • Λύʔηϯτදهʹܗ͢Δࡍʹ100ഒͯ͠Ͳ͏ʹ͔͠Α͏ͱ͠ ͍͚ͯͳ͍ • NumberFormatterͳͲΛ͍ͬͯͩ͘͞ • ༗ޮܻͷࢦఆศར͕ͩɺจࣈྻͷ͞Λ੍ݶͯ͘͠Εͳ͍ͷͰҙ
͕ඞཁ • maximumFractionDigits ͱಉ͡Α͏ͳͷͱࢥͬͯ͠·͏ϫφ • ςετΛॻ͍ͯ҆৺͠Α͏ 00
ࣗݾհ glass fi ber ϐΫγϒגࣜձࣾ ৽نࣄۀ෦ iOSΤϯδχΞ • 20238݄ த్ೖࣾ
• Pastelaͱ͍͏͓ֆඳ͖ΞϓϦͷ։ൃʹैࣄ • લ৬ήʔϜ։ൃऀ • C++, C#Λओʹ༻ • 6લ·ͰiOS༻ήʔϜ࡞͍ͬͯͨ(iOS3ʙ7ͷ͜Ζ) • ϒϥϯΫΛຒΊΔͨΊमߦத 00
00 ͓·͚
ුಈখͷதΛݟΔ • ුಈখ: IEEE754 (Double : ഒਫ਼ɺFloat: ୯ਫ਼) • ුಈখͷܭࢉΛϏοτ୯ҐͰݟΕΔπʔϧ
• IEEE 754 Calculator (http://weitz.de/ieee/) 00
ුಈখͷதΛݟΔ • SwiftͰ .bitPatternͰුಈখͷදݱΛ ֬ೝͰ͖Δ • .exponentBitPatternͱ.signi fi candBitPatternͰࢦ෦ͱԾ෦Λݸผ ʹݟΔ͜ͱՄೳ
00 print("\(String(0.523.bitPattern, radix: 2))") print("\(String(0.523.exponentBitPattern, radix: 2))") print("\(String(0.523.significandBitPattern, radix: 2))") 11111111100000101111000110101001111110111110011101101100100011 1111111110 101111000110101001111110111110011101101100100011
None