Add ToUpperOrdinal and ToLowerOrdinal casing APIs

src/coreclr/vm/wasm/browser/callhelpers-pinvoke.cpp

@@ -45,6 +45,7 @@ extern "C" {
     int32_t GlobalizationNative_IndexOf (void *, void *, int32_t, void *, int32_t, int32_t, void *);
     void GlobalizationNative_InitICUFunctions (void *, void *, void *, void *);
     void GlobalizationNative_InitOrdinalCasingPage (int32_t, void *);
+    void GlobalizationNative_InitOrdinalLowerCasingPage (int32_t, void *);
     int32_t GlobalizationNative_IsNormalized (int32_t, void *, int32_t);
     int32_t GlobalizationNative_IsPredefinedLocale (void *);
     int32_t GlobalizationNative_LastIndexOf (void *, void *, int32_t, void *, int32_t, int32_t, void *);
@@ -182,6 +183,7 @@ static const Entry s_libSystem_Globalization_Native [] = {
     DllImportEntry(GlobalizationNative_IndexOf) // System.Private.CoreLib
     DllImportEntry(GlobalizationNative_InitICUFunctions) // System.Private.CoreLib
     DllImportEntry(GlobalizationNative_InitOrdinalCasingPage) // System.Private.CoreLib
+    DllImportEntry(GlobalizationNative_InitOrdinalLowerCasingPage) // System.Private.CoreLib
     DllImportEntry(GlobalizationNative_IsNormalized) // System.Private.CoreLib
     DllImportEntry(GlobalizationNative_IsPredefinedLocale) // System.Private.CoreLib
     DllImportEntry(GlobalizationNative_LastIndexOf) // System.Private.CoreLib

src/coreclr/vm/wasm/wasi/callhelpers-pinvoke.cpp

@@ -44,6 +44,7 @@ extern "C" {
     int32_t GlobalizationNative_IndexOf (void *, void *, int32_t, void *, int32_t, int32_t, void *);
     void GlobalizationNative_InitICUFunctions (void *, void *, void *, void *);
     void GlobalizationNative_InitOrdinalCasingPage (int32_t, void *);
+    void GlobalizationNative_InitOrdinalLowerCasingPage (int32_t, void *);
     int32_t GlobalizationNative_IsNormalized (int32_t, void *, int32_t);
     int32_t GlobalizationNative_IsPredefinedLocale (void *);
     int32_t GlobalizationNative_LastIndexOf (void *, void *, int32_t, void *, int32_t, int32_t, void *);
@@ -232,6 +233,7 @@ static const Entry s_libSystem_Globalization_Native [] = {
     DllImportEntry(GlobalizationNative_IndexOf) // System.Private.CoreLib
     DllImportEntry(GlobalizationNative_InitICUFunctions) // System.Private.CoreLib
     DllImportEntry(GlobalizationNative_InitOrdinalCasingPage) // System.Private.CoreLib
+    DllImportEntry(GlobalizationNative_InitOrdinalLowerCasingPage) // System.Private.CoreLib
     DllImportEntry(GlobalizationNative_IsNormalized) // System.Private.CoreLib
     DllImportEntry(GlobalizationNative_IsPredefinedLocale) // System.Private.CoreLib
     DllImportEntry(GlobalizationNative_LastIndexOf) // System.Private.CoreLib

src/libraries/Common/src/Interop/Interop.Casing.cs

@@ -21,5 +21,8 @@ internal static partial class Globalization
 
         [LibraryImport(Libraries.GlobalizationNative, EntryPoint = "GlobalizationNative_InitOrdinalCasingPage", StringMarshalling = StringMarshalling.Utf16)]
         internal static unsafe partial void InitOrdinalCasingPage(int pageNumber, char* pTarget);
+
+        [LibraryImport(Libraries.GlobalizationNative, EntryPoint = "GlobalizationNative_InitOrdinalLowerCasingPage", StringMarshalling = StringMarshalling.Utf16)]
+        internal static unsafe partial void InitOrdinalLowerCasingPage(int pageNumber, char* pTarget);
     }
 }

src/libraries/System.Memory/ref/System.Memory.cs

@@ -499,8 +499,10 @@ public static void Sort<TKey, TValue, TComparer>(this System.Span<TKey> keys, Sy
         public static bool StartsWith<T>(this System.ReadOnlySpan<T> span, T value, System.Collections.Generic.IEqualityComparer<T>? comparer = null) { throw null; }
         public static int ToLower(this System.ReadOnlySpan<char> source, System.Span<char> destination, System.Globalization.CultureInfo? culture) { throw null; }
         public static int ToLowerInvariant(this System.ReadOnlySpan<char> source, System.Span<char> destination) { throw null; }
+        public static int ToLowerOrdinal(this System.ReadOnlySpan<char> source, System.Span<char> destination) { throw null; }
         public static int ToUpper(this System.ReadOnlySpan<char> source, System.Span<char> destination, System.Globalization.CultureInfo? culture) { throw null; }
         public static int ToUpperInvariant(this System.ReadOnlySpan<char> source, System.Span<char> destination) { throw null; }
+        public static int ToUpperOrdinal(this System.ReadOnlySpan<char> source, System.Span<char> destination) { throw null; }
         public static System.Memory<char> Trim(this System.Memory<char> memory) { throw null; }
         public static System.ReadOnlyMemory<char> Trim(this System.ReadOnlyMemory<char> memory) { throw null; }
         public static System.ReadOnlySpan<char> Trim(this System.ReadOnlySpan<char> span) { throw null; }

src/libraries/System.Private.CoreLib/src/System/Char.cs

@@ -529,6 +529,14 @@ public static char ToUpper(char c)
         // Converts a character to upper-case for invariant culture.
         public static char ToUpperInvariant(char c) => TextInfo.ToUpperInvariant(c);
 
+        /// <summary>
+        /// Converts a character to uppercase using the casing rules used by
+        /// <see cref="StringComparison.OrdinalIgnoreCase"/> comparisons.
+        /// </summary>
+        /// <param name="c">The character to convert.</param>
+        /// <returns>The uppercase equivalent of <paramref name="c"/>.</returns>
+        public static char ToUpperOrdinal(char c) => TextInfo.ToUpperOrdinal(c);
+
         /*===================================ToLower====================================
         **
         ==============================================================================*/
@@ -558,6 +566,13 @@ public static char ToLower(char c)
         // Converts a character to lower-case for invariant culture.
         public static char ToLowerInvariant(char c) => TextInfo.ToLowerInvariant(c);
 
+        /// <summary>
+        /// Converts a character to lowercase using ordinal (simple, one-to-one) casing rules.
+        /// </summary>
+        /// <param name="c">The character to convert.</param>
+        /// <returns>The lowercase equivalent of <paramref name="c"/>.</returns>
+        public static char ToLowerOrdinal(char c) => TextInfo.ToLowerOrdinal(c);
+
         //
         // IConvertible implementation
         //

src/libraries/System.Private.CoreLib/src/System/Globalization/Ordinal.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Buffers;
 using System.Diagnostics;
 using System.Numerics;
 using System.Runtime.CompilerServices;
@@ -707,5 +708,87 @@ internal static int ToUpperOrdinal(ReadOnlySpan<char> source, Span<char> destina
             OrdinalCasing.ToUpperOrdinal(source, destination);
             return source.Length;
         }
+
+        internal static int ToLowerOrdinal(ReadOnlySpan<char> source, Span<char> destination)
+        {
+            if (source.Overlaps(destination))
+                ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_SpanOverlappedOperation);
+
+            // Assuming that changing case does not affect length
+            if (destination.Length < source.Length)
+                return -1;
+
+            if (GlobalizationMode.Invariant)
+            {
+                InvariantModeCasing.ToLower(source, destination);
+                PreserveOrdinalLowerCasingClass(source, destination);
+                return source.Length;
+            }
+
+            if (GlobalizationMode.UseNls)
+            {
+                TextInfo.Invariant.ChangeCaseToLower(source, destination); // this is the best so far for NLS.
+                PreserveOrdinalLowerCasingClass(source, destination);
+                return source.Length;
+            }
+
+            OrdinalCasing.ToLowerOrdinal(source, destination);
+            return source.Length;
+        }
+
+        // Ordinal lower casing must never move a character out of its ordinal upper-casing class, otherwise it
+        // would stop being consistent with OrdinalIgnoreCase (for example the Kelvin, Ohm and Angstrom signs). The
+        // ICU ordinal table encodes this directly, but invariant and NLS simple lowering do not, so restore any
+        // BMP character whose simple lower mapping changed its ordinal upper-casing form.
+        private static void PreserveOrdinalLowerCasingClass(ReadOnlySpan<char> source, Span<char> destination)
+        {
+            // Upper-case the original text and the lowered result once over the whole span instead of calling
+            // TextInfo.ToUpperOrdinal per character. Per-character upper-casing is expensive under NLS, where each
+            // non-ASCII character would otherwise route through a separate invariant ChangeCase call.
+            const int StackAllocThreshold = 256;
+
+            char[]? sourceUpperRented = null;
+            char[]? loweredUpperRented = null;
+
+            Span<char> sourceUpper = source.Length <= StackAllocThreshold
+                ? stackalloc char[StackAllocThreshold]
+                : (sourceUpperRented = ArrayPool<char>.Shared.Rent(source.Length));
+            sourceUpper = sourceUpper.Slice(0, source.Length);
+
+            Span<char> loweredUpper = source.Length <= StackAllocThreshold
+                ? stackalloc char[StackAllocThreshold]
+                : (loweredUpperRented = ArrayPool<char>.Shared.Rent(source.Length));
+            loweredUpper = loweredUpper.Slice(0, source.Length);
+
+            ToUpperOrdinal(source, sourceUpper);
+            ToUpperOrdinal(destination.Slice(0, source.Length), loweredUpper);
+
+            for (int i = 0; i < source.Length; i++)
+            {
+                char c = source[i];
+
+                // The special characters are all single BMP scalars, so surrogate pairs never need adjustment.
+                if (char.IsHighSurrogate(c) && i + 1 < source.Length && char.IsLowSurrogate(source[i + 1]))
+                {
+                    i++;
+                    continue;
+                }
+
+                if (destination[i] != c && !char.IsAscii(c) && sourceUpper[i] != loweredUpper[i])
+                {
+                    destination[i] = c;
+                }
+            }
+
+            if (sourceUpperRented is not null)
+            {
+                ArrayPool<char>.Shared.Return(sourceUpperRented);
+            }
+
+            if (loweredUpperRented is not null)
+            {
+                ArrayPool<char>.Shared.Return(loweredUpperRented);
+            }
+        }
     }
 }

src/libraries/System.Private.CoreLib/src/System/Globalization/OrdinalCasing.Icu.cs

@@ -43,6 +43,35 @@ internal static partial class OrdinalCasing
         // Every cell is array of 512 character for uppercasing mapping.
         private static readonly ushort[]?[] s_casingTable = InitCasingTable();
 
+        // s_lowerBasicLatin covers the lower casing for the Basic Latin & C0 Controls range.
+        // We don't lazily initialize this range because it is the most commonly used range and we'll cache it anyway very early.
+        private static readonly ushort[] s_lowerBasicLatin =
+        [
+            // Lower Casing
+
+            /* 0000-000f */  0x0000, 0x0001, 0x0002, 0x0003, 0x0004, 0x0005, 0x0006, 0x0007, 0x0008, 0x0009, 0x000a, 0x000b, 0x000c, 0x000d, 0x000e, 0x000f,
+            /* 0010-001f */  0x0010, 0x0011, 0x0012, 0x0013, 0x0014, 0x0015, 0x0016, 0x0017, 0x0018, 0x0019, 0x001a, 0x001b, 0x001c, 0x001d, 0x001e, 0x001f,
+            /* 0020-002f */  0x0020, 0x0021, 0x0022, 0x0023, 0x0024, 0x0025, 0x0026, 0x0027, 0x0028, 0x0029, 0x002a, 0x002b, 0x002c, 0x002d, 0x002e, 0x002f,
+            /* 0030-003f */  0x0030, 0x0031, 0x0032, 0x0033, 0x0034, 0x0035, 0x0036, 0x0037, 0x0038, 0x0039, 0x003a, 0x003b, 0x003c, 0x003d, 0x003e, 0x003f,
+            /* 0040-004f */  0x0040, 0x0061, 0x0062, 0x0063, 0x0064, 0x0065, 0x0066, 0x0067, 0x0068, 0x0069, 0x006a, 0x006b, 0x006c, 0x006d, 0x006e, 0x006f,
+            /* 0050-005f */  0x0070, 0x0071, 0x0072, 0x0073, 0x0074, 0x0075, 0x0076, 0x0077, 0x0078, 0x0079, 0x007a, 0x005b, 0x005c, 0x005d, 0x005e, 0x005f,
+            /* 0060-006f */  0x0060, 0x0061, 0x0062, 0x0063, 0x0064, 0x0065, 0x0066, 0x0067, 0x0068, 0x0069, 0x006a, 0x006b, 0x006c, 0x006d, 0x006e, 0x006f,
+            /* 0070-007f */  0x0070, 0x0071, 0x0072, 0x0073, 0x0074, 0x0075, 0x0076, 0x0077, 0x0078, 0x0079, 0x007a, 0x007b, 0x007c, 0x007d, 0x007e, 0x007f,
+            /* 0080-008f */  0x0080, 0x0081, 0x0082, 0x0083, 0x0084, 0x0085, 0x0086, 0x0087, 0x0088, 0x0089, 0x008a, 0x008b, 0x008c, 0x008d, 0x008e, 0x008f,
+            /* 0090-009f */  0x0090, 0x0091, 0x0092, 0x0093, 0x0094, 0x0095, 0x0096, 0x0097, 0x0098, 0x0099, 0x009a, 0x009b, 0x009c, 0x009d, 0x009e, 0x009f,
+            /* 00a0-00af */  0x00a0, 0x00a1, 0x00a2, 0x00a3, 0x00a4, 0x00a5, 0x00a6, 0x00a7, 0x00a8, 0x00a9, 0x00aa, 0x00ab, 0x00ac, 0x00ad, 0x00ae, 0x00af,
+            /* 00b0-00bf */  0x00b0, 0x00b1, 0x00b2, 0x00b3, 0x00b4, 0x00b5, 0x00b6, 0x00b7, 0x00b8, 0x00b9, 0x00ba, 0x00bb, 0x00bc, 0x00bd, 0x00be, 0x00bf,
+            /* 00c0-00cf */  0x00e0, 0x00e1, 0x00e2, 0x00e3, 0x00e4, 0x00e5, 0x00e6, 0x00e7, 0x00e8, 0x00e9, 0x00ea, 0x00eb, 0x00ec, 0x00ed, 0x00ee, 0x00ef,
+            /* 00d0-00df */  0x00f0, 0x00f1, 0x00f2, 0x00f3, 0x00f4, 0x00f5, 0x00f6, 0x00d7, 0x00f8, 0x00f9, 0x00fa, 0x00fb, 0x00fc, 0x00fd, 0x00fe, 0x00df,
+            /* 00e0-00ef */  0x00e0, 0x00e1, 0x00e2, 0x00e3, 0x00e4, 0x00e5, 0x00e6, 0x00e7, 0x00e8, 0x00e9, 0x00ea, 0x00eb, 0x00ec, 0x00ed, 0x00ee, 0x00ef,
+            /* 00f0-00ff */  0x00f0, 0x00f1, 0x00f2, 0x00f3, 0x00f4, 0x00f5, 0x00f6, 0x00f7, 0x00f8, 0x00f9, 0x00fa, 0x00fb, 0x00fc, 0x00fd, 0x00fe, 0x00ff,
+        ];
+
+        // s_lowerCasingTable mirrors s_casingTable but holds the simple lower casing mapping for the BMP.
+        // It is pre-seeded with the shared NoCasingPage for the permanently uncased pages (see InitLowerCasingTable);
+        // remaining pages are initialized lazily through ICU and identity pages collapse to the shared NoCasingPage.
+        private static readonly ushort[]?[] s_lowerCasingTable = InitLowerCasingTable();
+
         /*
          The table is initialized to:
         {
@@ -172,6 +201,57 @@ internal static void ToUpperOrdinal(ReadOnlySpan<char> source, Span<char> destin
             }
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static char ToLower(char c)
+        {
+            int pageNumber = ((int)c) >> 8;
+            if (pageNumber == 0) // optimize for ASCII range
+            {
+                return (char)s_lowerBasicLatin[(int)c];
+            }
+
+            ushort[]? casingTable = s_lowerCasingTable[pageNumber];
+
+            if (casingTable == NoCasingPage)
+            {
+                return c;
+            }
+
+            casingTable ??= InitOrdinalLowerCasingPage(pageNumber);
+
+            return (char)casingTable[((int)c) & 0xFF];
+        }
+
+        internal static void ToLowerOrdinal(ReadOnlySpan<char> source, Span<char> destination)
+        {
+            Debug.Assert(!GlobalizationMode.Invariant);
+            Debug.Assert(!GlobalizationMode.UseNls);
+
+            for (int i = 0; i < source.Length; i++)
+            {
+                char c = source[i];
+                if (c <= '\u00FF') // optimize ASCII/Latin
+                {
+                    destination[i] = (char)s_lowerBasicLatin[c];
+                    continue;
+                }
+
+                if (char.IsHighSurrogate(c) && i < source.Length - 1)
+                {
+                    char cl = source[i + 1];
+                    if (char.IsLowSurrogate(cl))
+                    {
+                        // well formed surrogates
+                        SurrogateCasing.ToLower(c, cl, out destination[i], out destination[i + 1]);
+                        i++; // skip the low surrogate
+                        continue;
+                    }
+                }
+
+                destination[i] = ToLower(c);
+            }
+        }
+
         internal static int CompareStringIgnoreCase(ref char strA, int lengthA, ref char strB, int lengthB)
         {
             Debug.Assert(!GlobalizationMode.Invariant);
@@ -428,5 +508,46 @@ private static unsafe ushort[] InitOrdinalCasingPage(int pageNumber)
             Volatile.Write(ref s_casingTable[pageNumber], casingTable);
             return casingTable;
         }
+
+        private static ushort[]?[] InitLowerCasingTable()
+        {
+            // Reuse the upper-casing NoCasing bitmap to pre-seed the lower-casing table. Every page that bitmap
+            // marks (the permanently uncased CJK/Hangul/PUA blocks) is also identity under lower casing, so seeding
+            // these pages with the shared NoCasingPage avoids first-use native calls without risking a wrong mapping.
+            ushort[]?[] table = new ushort[]?[s_casingTableInit.Length * 8];
+            for (int i = 0; i < s_casingTableInit.Length * 8; ++i)
+            {
+                // The bits are in reverse order
+                byte val = (byte)(s_casingTableInit[i / 8] >> (7 - (i % 8)));
+                if ((val & 1) == 1)
+                    table[i] = NoCasingPage;
+            }
+            table[0] = s_lowerBasicLatin;
+            return table;
+        }
+
+        private static unsafe ushort[] InitOrdinalLowerCasingPage(int pageNumber)
+        {
+            Debug.Assert(pageNumber > 0 && pageNumber < 256);
+
+            ushort[] casingTable = new ushort[256];
+            fixed (ushort* table = casingTable)
+            {
+                char* pTable = (char*)table;
+                Interop.Globalization.InitOrdinalLowerCasingPage(pageNumber, pTable);
+            }
+
+            // If the page doesn't change any character, collapse it to the shared NoCasingPage to avoid
+            // retaining the 512-byte buffer. We still return the fully populated table for the current lookup.
+            int pageBase = pageNumber << 8;
+            int i = 0;
+            while (i < 256 && casingTable[i] == (ushort)(pageBase + i))
+            {
+                i++;
+            }
+
+            Volatile.Write(ref s_lowerCasingTable[pageNumber], i == 256 ? NoCasingPage : casingTable);
+            return casingTable;
+        }
     }
 }

src/libraries/System.Private.CoreLib/src/System/Globalization/TextInfo.cs

@@ -204,6 +204,33 @@ internal static char ToUpperOrdinal(char c)
             return OrdinalCasing.ToUpper(c);
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static char ToLowerOrdinal(char c)
+        {
+            if (GlobalizationMode.Invariant)
+            {
+                return char.IsAscii(c)
+                    ? ToLowerAsciiInvariant(c)
+                    : PreserveOrdinalLowerCasingClass(c, InvariantModeCasing.ToLower(c));
+            }
+
+            if (GlobalizationMode.UseNls)
+            {
+                return char.IsAscii(c)
+                    ? ToLowerAsciiInvariant(c)
+                    : PreserveOrdinalLowerCasingClass(c, Invariant.ChangeCase(c, toUpper: false));
+            }
+
+            return OrdinalCasing.ToLower(c);
+        }
+
+        // Ordinal lower casing must never move a character out of its ordinal upper-casing class, otherwise it
+        // would stop being consistent with OrdinalIgnoreCase (for example the Kelvin, Ohm and Angstrom signs). The
+        // ICU ordinal table encodes this directly, but invariant and NLS simple lowering do not, so keep the original
+        // character whenever its simple lower mapping would change its ordinal upper-casing form.
+        private static char PreserveOrdinalLowerCasingClass(char c, char lower) =>
+            lower == c || ToUpperOrdinal(lower) == ToUpperOrdinal(c) ? lower : c;
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal void ChangeCaseToLower(ReadOnlySpan<char> source, Span<char> destination)
         {