Speed up utf8 decoding

lib/std/unicode.zig

@@ -3,7 +3,7 @@
 // This file is part of [zig](https://ziglang.org/), which is MIT licensed.
 // The MIT license requires this copyright notice to be included in all copies
 // and substantial portions of the software.
-const std = @import("./std.zig");
+const std = @import("std");
 const builtin = @import("builtin");
 const assert = std.debug.assert;
 const testing = std.testing;
@@ -23,11 +23,12 @@ pub fn utf8CodepointSequenceLength(c: u21) !u3 {
 /// returns a number 1-4 indicating the total length of the codepoint in bytes.
 /// If this byte does not match the form of a UTF-8 start byte, returns Utf8InvalidStartByte.
 pub fn utf8ByteSequenceLength(first_byte: u8) !u3 {
-    return switch (@clz(u8, ~first_byte)) {
-        0 => 1,
-        2 => 2,
-        3 => 3,
-        4 => 4,
+    // The switch is optimized much better than a "smart" approach using @clz
+    return switch (first_byte) {
+        0b0000_0000...0b0111_1111 => 1,
+        0b1100_0000...0b1101_1111 => 2,
+        0b1110_0000...0b1110_1111 => 3,
+        0b1111_0000...0b1111_0111 => 4,
         else => error.Utf8InvalidStartByte,
     };
 }
@@ -106,6 +107,7 @@ const Utf8Decode3Error = error{
     Utf8OverlongEncoding,
     Utf8EncodesSurrogateHalf,
 };
+
 pub fn utf8Decode3(bytes: []const u8) Utf8Decode3Error!u21 {
     assert(bytes.len == 3);
     assert(bytes[0] & 0b11110000 == 0b11100000);
@@ -153,6 +155,50 @@ pub fn utf8Decode4(bytes: []const u8) Utf8Decode4Error!u21 {
     return value;
 }
 
+/// Returns true if the given unicode codepoint can be encoded in UTF-8.
+pub fn isValidCodepoint(value: u21) bool {
+    return switch (value) {
+        0xD800...0xDFFF => false, // Surrogates range
+        0x110000...0x1FFFFF => false, // Above the maximum codepoint value
+        else => true,
+    };
+}
+
+/// Returns the length of a supplied UTF-8 string literal in terms of unicode
+/// codepoints.
+/// Errors: if this string cannot be decoded.
+pub fn utf8CountCodepoints(s: []const u8) !usize {
+    var len: usize = 0;
+
+    const N = @sizeOf(usize);
+    const MASK = 0x80 * (std.math.maxInt(usize) / 0xff);
+
+    var i: usize = 0;
+    while (i < s.len) {
+        // Fast path for ASCII sequences
+        while (i + N <= s.len) : (i += N) {
+            const v = mem.readIntNative(usize, s[i..][0..N]);
+            if (v & MASK != 0) break;
+            len += N;
+        }
+
+        if (i < s.len) {
+            const n = try utf8ByteSequenceLength(s[i]);
+            if (i + n > s.len) return error.TruncatedInput;
+
+            switch (n) {
+                1 => {}, // ASCII, no validation needed
+                else => _ = try utf8Decode(s[i .. i + n]),
+            }
+
+            i += n;
+            len += 1;
+        }
+    }
+
+    return len;
+}
+
 pub fn utf8ValidateSlice(s: []const u8) bool {
     var i: usize = 0;
     while (i < s.len) {
@@ -757,3 +803,31 @@ test "utf8ToUtf16LeStringLiteral" {
         testing.expect(utf16[2] == 0);
     }
 }
+
+fn testUtf8CountCodepoints() !void {
+    testing.expectEqual(@as(usize, 10), try utf8CountCodepoints("abcdefghij"));
+    testing.expectEqual(@as(usize, 10), try utf8CountCodepoints("äåéëþüúíóö"));
+    testing.expectEqual(@as(usize, 5), try utf8CountCodepoints("こんにちは"));
+    // testing.expectError(error.Utf8EncodesSurrogateHalf, utf8CountCodepoints("\xED\xA0\x80"));
+}
+
+test "utf8 count codepoints" {
+    try testUtf8CountCodepoints();
+    comptime testUtf8CountCodepoints() catch unreachable;
+}
+
+fn testisValidCodepoint() !void {
+    testing.expect(isValidCodepoint('e'));
+    testing.expect(isValidCodepoint('ë'));
+    testing.expect(isValidCodepoint('は'));
+    testing.expect(isValidCodepoint(0xe000));
+    testing.expect(isValidCodepoint(0x10ffff));
+    testing.expect(!isValidCodepoint(0xd800));
+    testing.expect(!isValidCodepoint(0xdfff));
+    testing.expect(!isValidCodepoint(0x110000));
+}
+
+test "utf8 valid codepoint" {
+    try testisValidCodepoint();
+    comptime testisValidCodepoint() catch unreachable;
+}

lib/std/unicode/UTF-8-demo.txt

@@ -0,0 +1,212 @@
+
+UTF-8 encoded sample plain-text file
+‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
+
+Markus Kuhn [ˈmaʳkʊs kuːn] <https://www.cl.cam.ac.uk/~mgk25/> — 2002-07-25
+
+
+The ASCII compatible UTF-8 encoding used in this plain-text file
+is defined in Unicode, ISO 10646-1, and RFC 2279.
+
+
+Using Unicode/UTF-8, you can write in emails and source code things such as
+
+Mathematics and sciences:
+
+  ∮ E⋅da = Q,  n → ∞, ∑ f(i) = ∏ g(i),      ⎧⎡⎛┌─────┐⎞⎤⎫
+                                            ⎪⎢⎜│a²+b³ ⎟⎥⎪
+  ∀x∈ℝ: ⌈x⌉ = −⌊−x⌋, α ∧ ¬β = ¬(¬α ∨ β),    ⎪⎢⎜│───── ⎟⎥⎪
+                                            ⎪⎢⎜⎷ c₈   ⎟⎥⎪
+  ℕ ⊆ ℕ₀ ⊂ ℤ ⊂ ℚ ⊂ ℝ ⊂ ℂ,                   ⎨⎢⎜       ⎟⎥⎬
+                                            ⎪⎢⎜ ∞     ⎟⎥⎪
+  ⊥ < a ≠ b ≡ c ≤ d ≪ ⊤ ⇒ (⟦A⟧ ⇔ ⟪B⟫),      ⎪⎢⎜ ⎲     ⎟⎥⎪
+                                            ⎪⎢⎜ ⎳aⁱ-bⁱ⎟⎥⎪
+  2H₂ + O₂ ⇌ 2H₂O, R = 4.7 kΩ, ⌀ 200 mm     ⎩⎣⎝i=1    ⎠⎦⎭
+
+Linguistics and dictionaries:
+
+  ði ıntəˈnæʃənəl fəˈnɛtık əsoʊsiˈeıʃn
+  Y [ˈʏpsilɔn], Yen [jɛn], Yoga [ˈjoːgɑ]
+
+APL:
+
+  ((V⍳V)=⍳⍴V)/V←,V    ⌷←⍳→⍴∆∇⊃‾⍎⍕⌈
+
+Nicer typography in plain text files:
+
+  ╔══════════════════════════════════════════╗
+  ║                                          ║
+  ║   • ‘single’ and “double” quotes         ║
+  ║                                          ║
+  ║   • Curly apostrophes: “We’ve been here” ║
+  ║                                          ║
+  ║   • Latin-1 apostrophe and accents: '´`  ║
+  ║                                          ║
+  ║   • ‚deutsche‘ „Anführungszeichen“       ║
+  ║                                          ║
+  ║   • †, ‡, ‰, •, 3–4, —, −5/+5, ™, …      ║
+  ║                                          ║
+  ║   • ASCII safety test: 1lI|, 0OD, 8B     ║
+  ║                      ╭─────────╮         ║
+  ║   • the euro symbol: │ 14.95 € │         ║
+  ║                      ╰─────────╯         ║
+  ╚══════════════════════════════════════════╝
+
+Combining characters:
+
+  STARGΛ̊TE SG-1, a = v̇ = r̈, a⃑ ⊥ b⃑
+
+Greek (in Polytonic):
+
+  The Greek anthem:
+
+  Σὲ γνωρίζω ἀπὸ τὴν κόψη
+  τοῦ σπαθιοῦ τὴν τρομερή,
+  σὲ γνωρίζω ἀπὸ τὴν ὄψη
+  ποὺ μὲ βία μετράει τὴ γῆ.
+
+  ᾿Απ᾿ τὰ κόκκαλα βγαλμένη
+  τῶν ῾Ελλήνων τὰ ἱερά
+  καὶ σὰν πρῶτα ἀνδρειωμένη
+  χαῖρε, ὦ χαῖρε, ᾿Ελευθεριά!
+
+  From a speech of Demosthenes in the 4th century BC:
+
+  Οὐχὶ ταὐτὰ παρίσταταί μοι γιγνώσκειν, ὦ ἄνδρες ᾿Αθηναῖοι,
+  ὅταν τ᾿ εἰς τὰ πράγματα ἀποβλέψω καὶ ὅταν πρὸς τοὺς
+  λόγους οὓς ἀκούω· τοὺς μὲν γὰρ λόγους περὶ τοῦ
+  τιμωρήσασθαι Φίλιππον ὁρῶ γιγνομένους, τὰ δὲ πράγματ᾿
+  εἰς τοῦτο προήκοντα,  ὥσθ᾿ ὅπως μὴ πεισόμεθ᾿ αὐτοὶ
+  πρότερον κακῶς σκέψασθαι δέον. οὐδέν οὖν ἄλλο μοι δοκοῦσιν
+  οἱ τὰ τοιαῦτα λέγοντες ἢ τὴν ὑπόθεσιν, περὶ ἧς βουλεύεσθαι,
+  οὐχὶ τὴν οὖσαν παριστάντες ὑμῖν ἁμαρτάνειν. ἐγὼ δέ, ὅτι μέν
+  ποτ᾿ ἐξῆν τῇ πόλει καὶ τὰ αὑτῆς ἔχειν ἀσφαλῶς καὶ Φίλιππον
+  τιμωρήσασθαι, καὶ μάλ᾿ ἀκριβῶς οἶδα· ἐπ᾿ ἐμοῦ γάρ, οὐ πάλαι
+  γέγονεν ταῦτ᾿ ἀμφότερα· νῦν μέντοι πέπεισμαι τοῦθ᾿ ἱκανὸν
+  προλαβεῖν ἡμῖν εἶναι τὴν πρώτην, ὅπως τοὺς συμμάχους
+  σώσομεν. ἐὰν γὰρ τοῦτο βεβαίως ὑπάρξῃ, τότε καὶ περὶ τοῦ
+  τίνα τιμωρήσεταί τις καὶ ὃν τρόπον ἐξέσται σκοπεῖν· πρὶν δὲ
+  τὴν ἀρχὴν ὀρθῶς ὑποθέσθαι, μάταιον ἡγοῦμαι περὶ τῆς
+  τελευτῆς ὁντινοῦν ποιεῖσθαι λόγον.
+
+  Δημοσθένους, Γ´ ᾿Ολυνθιακὸς
+
+Georgian:
+
+  From a Unicode conference invitation:
+
+  გთხოვთ ახლავე გაიაროთ რეგისტრაცია Unicode-ის მეათე საერთაშორისო
+  კონფერენციაზე დასასწრებად, რომელიც გაიმართება 10-12 მარტს,
+  ქ. მაინცში, გერმანიაში. კონფერენცია შეჰკრებს ერთად მსოფლიოს
+  ექსპერტებს ისეთ დარგებში როგორიცაა ინტერნეტი და Unicode-ი,
+  ინტერნაციონალიზაცია და ლოკალიზაცია, Unicode-ის გამოყენება
+  ოპერაციულ სისტემებსა, და გამოყენებით პროგრამებში, შრიფტებში,
+  ტექსტების დამუშავებასა და მრავალენოვან კომპიუტერულ სისტემებში.
+
+Russian:
+
+  From a Unicode conference invitation:
+
+  Зарегистрируйтесь сейчас на Десятую Международную Конференцию по
+  Unicode, которая состоится 10-12 марта 1997 года в Майнце в Германии.
+  Конференция соберет широкий круг экспертов по  вопросам глобального
+  Интернета и Unicode, локализации и интернационализации, воплощению и
+  применению Unicode в различных операционных системах и программных
+  приложениях, шрифтах, верстке и многоязычных компьютерных системах.
+
+Thai (UCS Level 2):
+
+  Excerpt from a poetry on The Romance of The Three Kingdoms (a Chinese
+  classic 'San Gua'):
+
+  [----------------------------|------------------------]
+    ๏ แผ่นดินฮั่นเสื่อมโทรมแสนสังเวช  พระปกเกศกองบู๊กู้ขึ้นใหม่
+  สิบสองกษัตริย์ก่อนหน้าแลถัดไป       สององค์ไซร้โง่เขลาเบาปัญญา
+    ทรงนับถือขันทีเป็นที่พึ่ง           บ้านเมืองจึงวิปริตเป็นนักหนา
+  โฮจิ๋นเรียกทัพทั่วหัวเมืองมา         หมายจะฆ่ามดชั่วตัวสำคัญ
+    เหมือนขับไสไล่เสือจากเคหา      รับหมาป่าเข้ามาเลยอาสัญ
+  ฝ่ายอ้องอุ้นยุแยกให้แตกกัน          ใช้สาวนั้นเป็นชนวนชื่นชวนใจ
+    พลันลิฉุยกุยกีกลับก่อเหตุ          ช่างอาเพศจริงหนาฟ้าร้องไห้
+  ต้องรบราฆ่าฟันจนบรรลัย           ฤๅหาใครค้ำชูกู้บรรลังก์ ฯ
+
+  (The above is a two-column text. If combining characters are handled
+  correctly, the lines of the second column should be aligned with the
+  | character above.)
+
+Ethiopian:
+
+  Proverbs in the Amharic language:
+
+  ሰማይ አይታረስ ንጉሥ አይከሰስ።
+  ብላ ካለኝ እንደአባቴ በቆመጠኝ።
+  ጌጥ ያለቤቱ ቁምጥና ነው።
+  ደሀ በሕልሙ ቅቤ ባይጠጣ ንጣት በገደለው።
+  የአፍ ወለምታ በቅቤ አይታሽም።
+  አይጥ በበላ ዳዋ ተመታ።
+  ሲተረጉሙ ይደረግሙ።
+  ቀስ በቀስ፥ ዕንቁላል በእግሩ ይሄዳል።
+  ድር ቢያብር አንበሳ ያስር።
+  ሰው እንደቤቱ እንጅ እንደ ጉረቤቱ አይተዳደርም።
+  እግዜር የከፈተውን ጉሮሮ ሳይዘጋው አይድርም።
+  የጎረቤት ሌባ፥ ቢያዩት ይስቅ ባያዩት ያጠልቅ።
+  ሥራ ከመፍታት ልጄን ላፋታት።
+  ዓባይ ማደሪያ የለው፥ ግንድ ይዞ ይዞራል።
+  የእስላም አገሩ መካ የአሞራ አገሩ ዋርካ።
+  ተንጋሎ ቢተፉ ተመልሶ ባፉ።
+  ወዳጅህ ማር ቢሆን ጨርስህ አትላሰው።
+  እግርህን በፍራሽህ ልክ ዘርጋ።
+
+Runes:
+
+  ᚻᛖ ᚳᚹᚫᚦ ᚦᚫᛏ ᚻᛖ ᛒᚢᛞᛖ ᚩᚾ ᚦᚫᛗ ᛚᚪᚾᛞᛖ ᚾᚩᚱᚦᚹᛖᚪᚱᛞᚢᛗ ᚹᛁᚦ ᚦᚪ ᚹᛖᛥᚫ
+
+  (Old English, which transcribed into Latin reads 'He cwaeth that he
+  bude thaem lande northweardum with tha Westsae.' and means 'He said
+  that he lived in the northern land near the Western Sea.')
+
+Braille:
+
+  ⡌⠁⠧⠑ ⠼⠁⠒  ⡍⠜⠇⠑⠹⠰⠎ ⡣⠕⠌
+
+  ⡍⠜⠇⠑⠹ ⠺⠁⠎ ⠙⠑⠁⠙⠒ ⠞⠕ ⠃⠑⠛⠔ ⠺⠊⠹⠲ ⡹⠻⠑ ⠊⠎ ⠝⠕ ⠙⠳⠃⠞
+  ⠱⠁⠞⠑⠧⠻ ⠁⠃⠳⠞ ⠹⠁⠞⠲ ⡹⠑ ⠗⠑⠛⠊⠌⠻ ⠕⠋ ⠙⠊⠎ ⠃⠥⠗⠊⠁⠇ ⠺⠁⠎
+  ⠎⠊⠛⠝⠫ ⠃⠹ ⠹⠑ ⠊⠇⠻⠛⠹⠍⠁⠝⠂ ⠹⠑ ⠊⠇⠻⠅⠂ ⠹⠑ ⠥⠝⠙⠻⠞⠁⠅⠻⠂
+  ⠁⠝⠙ ⠹⠑ ⠡⠊⠑⠋ ⠍⠳⠗⠝⠻⠲ ⡎⠊⠗⠕⠕⠛⠑ ⠎⠊⠛⠝⠫ ⠊⠞⠲ ⡁⠝⠙
+  ⡎⠊⠗⠕⠕⠛⠑⠰⠎ ⠝⠁⠍⠑ ⠺⠁⠎ ⠛⠕⠕⠙ ⠥⠏⠕⠝ ⠰⡡⠁⠝⠛⠑⠂ ⠋⠕⠗ ⠁⠝⠹⠹⠔⠛ ⠙⠑
+  ⠡⠕⠎⠑ ⠞⠕ ⠏⠥⠞ ⠙⠊⠎ ⠙⠁⠝⠙ ⠞⠕⠲
+
+  ⡕⠇⠙ ⡍⠜⠇⠑⠹ ⠺⠁⠎ ⠁⠎ ⠙⠑⠁⠙ ⠁⠎ ⠁ ⠙⠕⠕⠗⠤⠝⠁⠊⠇⠲
+
+  ⡍⠔⠙⠖ ⡊ ⠙⠕⠝⠰⠞ ⠍⠑⠁⠝ ⠞⠕ ⠎⠁⠹ ⠹⠁⠞ ⡊ ⠅⠝⠪⠂ ⠕⠋ ⠍⠹
+  ⠪⠝ ⠅⠝⠪⠇⠫⠛⠑⠂ ⠱⠁⠞ ⠹⠻⠑ ⠊⠎ ⠏⠜⠞⠊⠊⠥⠇⠜⠇⠹ ⠙⠑⠁⠙ ⠁⠃⠳⠞
+  ⠁ ⠙⠕⠕⠗⠤⠝⠁⠊⠇⠲ ⡊ ⠍⠊⠣⠞ ⠙⠁⠧⠑ ⠃⠑⠲ ⠔⠊⠇⠔⠫⠂ ⠍⠹⠎⠑⠇⠋⠂ ⠞⠕
+  ⠗⠑⠛⠜⠙ ⠁ ⠊⠕⠋⠋⠔⠤⠝⠁⠊⠇ ⠁⠎ ⠹⠑ ⠙⠑⠁⠙⠑⠌ ⠏⠊⠑⠊⠑ ⠕⠋ ⠊⠗⠕⠝⠍⠕⠝⠛⠻⠹
+  ⠔ ⠹⠑ ⠞⠗⠁⠙⠑⠲ ⡃⠥⠞ ⠹⠑ ⠺⠊⠎⠙⠕⠍ ⠕⠋ ⠳⠗ ⠁⠝⠊⠑⠌⠕⠗⠎
+  ⠊⠎ ⠔ ⠹⠑ ⠎⠊⠍⠊⠇⠑⠆ ⠁⠝⠙ ⠍⠹ ⠥⠝⠙⠁⠇⠇⠪⠫ ⠙⠁⠝⠙⠎
+  ⠩⠁⠇⠇ ⠝⠕⠞ ⠙⠊⠌⠥⠗⠃ ⠊⠞⠂ ⠕⠗ ⠹⠑ ⡊⠳⠝⠞⠗⠹⠰⠎ ⠙⠕⠝⠑ ⠋⠕⠗⠲ ⡹⠳
+  ⠺⠊⠇⠇ ⠹⠻⠑⠋⠕⠗⠑ ⠏⠻⠍⠊⠞ ⠍⠑ ⠞⠕ ⠗⠑⠏⠑⠁⠞⠂ ⠑⠍⠏⠙⠁⠞⠊⠊⠁⠇⠇⠹⠂ ⠹⠁⠞
+  ⡍⠜⠇⠑⠹ ⠺⠁⠎ ⠁⠎ ⠙⠑⠁⠙ ⠁⠎ ⠁ ⠙⠕⠕⠗⠤⠝⠁⠊⠇⠲
+
+  (The first couple of paragraphs of "A Christmas Carol" by Dickens)
+
+Compact font selection example text:
+
+  ABCDEFGHIJKLMNOPQRSTUVWXYZ /0123456789
+  abcdefghijklmnopqrstuvwxyz £©µÀÆÖÞßéöÿ
+  –—‘“”„†•…‰™œŠŸž€ ΑΒΓΔΩαβγδω АБВГДабвгд
+  ∀∂∈ℝ∧∪≡∞ ↑↗↨↻⇣ ┐┼╔╘░►☺♀ fi�⑀₂ἠḂӥẄɐː⍎אԱა
+
+Greetings in various languages:
+
+  Hello world, Καλημέρα κόσμε, コンニチハ
+
+Box drawing alignment tests:                                          █
+                                                                      ▉
+  ╔══╦══╗  ┌──┬──┐  ╭──┬──╮  ╭──┬──╮  ┏━━┳━━┓  ┎┒┏┑   ╷  ╻ ┏┯┓ ┌┰┐    ▊ ╱╲╱╲╳╳╳
+  ║┌─╨─┐║  │╔═╧═╗│  │╒═╪═╕│  │╓─╁─╖│  ┃┌─╂─┐┃  ┗╃╄┙  ╶┼╴╺╋╸┠┼┨ ┝╋┥    ▋ ╲╱╲╱╳╳╳
+  ║│╲ ╱│║  │║   ║│  ││ │ ││  │║ ┃ ║│  ┃│ ╿ │┃  ┍╅╆┓   ╵  ╹ ┗┷┛ └┸┘    ▌ ╱╲╱╲╳╳╳
+  ╠╡ ╳ ╞╣  ├╢   ╟┤  ├┼─┼─┼┤  ├╫─╂─╫┤  ┣┿╾┼╼┿┫  ┕┛┖┚     ┌┄┄┐ ╎ ┏┅┅┓ ┋ ▍ ╲╱╲╱╳╳╳
+  ║│╱ ╲│║  │║   ║│  ││ │ ││  │║ ┃ ║│  ┃│ ╽ │┃  ░░▒▒▓▓██ ┊  ┆ ╎ ╏  ┇ ┋ ▎
+  ║└─╥─┘║  │╚═╤═╝│  │╘═╪═╛│  │╙─╀─╜│  ┃└─╂─┘┃  ░░▒▒▓▓██ ┊  ┆ ╎ ╏  ┇ ┋ ▏
+  ╚══╩══╝  └──┴──┘  ╰──┴──╯  ╰──┴──╯  ┗━━┻━━┛  ▗▄▖▛▀▜   └╌╌┘ ╎ ┗╍╍┛ ┋  ▁▂▃▄▅▆▇█
+                                               ▝▀▘▙▄▟