Add caseFolded to scalar properties

Author: Azoy

stdlib/private/StdlibUnicodeUnittest/UnicodeScalarProperties.swift

@@ -635,4 +635,53 @@ public let names: [Unicode.Scalar: String] = {
 
   return result
 }()
+
+//===----------------------------------------------------------------------===//
+// Case Folding
+//===----------------------------------------------------------------------===//
+
+func parseCaseFoldings(
+  _ data: String,
+  into result: inout [Unicode.Scalar: String]
+) {
+  for line in data.split(separator: "\n") {
+    // Skip comments
+    guard !line.hasPrefix("#") else {
+      continue
+    }
+    
+    let components = line.split(separator: ";")
+    
+    let status = components[1].filter { !$0.isWhitespace }
+    
+    // We only care about Common and Full case mappings.
+    guard status == "C" || status == "F" else {
+      continue
+    }
+    
+    let scalar = Unicode.Scalar(parseScalars(String(components[0])).lowerBound)!
+    
+    let mapping = components[2].split(separator: " ").map {
+      Unicode.Scalar(UInt32($0, radix: 16)!)!
+    }
+    
+    var mappingString = ""
+
+    for scalar in mapping {
+      mappingString.unicodeScalars.append(scalar)
+    }
+
+    result[scalar] = mappingString
+  }
+}
+
+public let caseFolding: [Unicode.Scalar: String] = {
+  var result: [Unicode.Scalar: String] = [:]
+
+  let caseFolding = readInputFile("CaseFolding.txt")
+  parseCaseFoldings(caseFolding, into: &result)
+
+  return result
+}()
+
 #endif

stdlib/public/SwiftShims/UnicodeData.h

@@ -108,6 +108,10 @@ const __swift_uint8_t *_swift_stdlib_getScriptExtensions(
                                                         __swift_uint32_t scalar,
                                                         __swift_uint8_t *count);
 
+SWIFT_RUNTIME_STDLIB_INTERNAL
+void _swift_stdlib_getCaseMapping(__swift_uint32_t scalar,
+                                  __swift_uint32_t *buffer);
+
 #ifdef __cplusplus
 } // extern "C"
 #endif

stdlib/public/core/UnicodeSPI.swift

@@ -165,3 +165,37 @@ extension Unicode.Scalar.Properties {
     return result
   }
 }
+
+//===----------------------------------------------------------------------===//
+// Case folding
+//===----------------------------------------------------------------------===//
+
+extension Unicode.Scalar.Properties {
+  @_spi(_Unicode)
+  @available(SwiftStdlib 5.7, *)
+  public var _caseFolded: String {
+    var buffer: (UInt32, UInt32, UInt32) = (.max, .max, .max)
+
+    withUnsafeMutableBytes(of: &buffer) {
+      // This is safe because the memory is already UInt32
+      let ptr = $0.baseAddress!.assumingMemoryBound(to: UInt32.self)
+      _swift_stdlib_getCaseMapping(_scalar.value, ptr)
+    }
+
+    var result = ""
+    // Max mapping is 3 scalars and the max UTF8 bytes of a scalar is 4.
+    result.reserveCapacity(12)
+
+    withUnsafeBytes(of: &buffer) {
+      for scalar in $0.bindMemory(to: UInt32.self) {
+        guard scalar != .max else {
+          break
+        }
+
+        result.unicodeScalars.append(Unicode.Scalar(scalar)!)
+      }
+    }
+
+    return result
+  }
+}

stdlib/public/stubs/Unicode/Common/CaseData.h

@@ -18,6 +18,7 @@
 #include "Common/ScalarPropsData.h"
 #endif
 
+#include "Common/CaseData.h"
 #include "Common/ScriptData.h"
 
 #else
@@ -510,3 +511,62 @@ const __swift_uint8_t *_swift_stdlib_getScriptExtensions(__swift_uint32_t scalar
   return _swift_stdlib_script_extensions_data + (scalarDataIdx & 0x7FF);
 #endif
 }
+
+SWIFT_RUNTIME_STDLIB_INTERNAL
+void _swift_stdlib_getCaseMapping(__swift_uint32_t scalar,
+                                  __swift_uint32_t *buffer) {
+#if !SWIFT_STDLIB_ENABLE_UNICODE_DATA
+  swift::swift_abortDisabledUnicodeSupport();
+#else
+  auto mphIdx = _swift_stdlib_getMphIdx(scalar, CASE_FOLD_LEVEL_COUNT,
+                                        _swift_stdlib_case_keys,
+                                        _swift_stdlib_case_ranks,
+                                        _swift_stdlib_case_sizes);
+  
+  auto caseValue = _swift_stdlib_case[mphIdx];
+  __swift_uint32_t hashedScalar = (caseValue << 43) >> 43;
+  
+  // If our scalar is not the original one we hashed, then this scalar has no
+  // case mapping. It maps to itself.
+  if (scalar != hashedScalar) {
+    buffer[0] = scalar;
+    return;
+  }
+  
+  // If the top bit is NOT set, then this scalar simply maps to another scalar.
+  // We have stored the distance to said scalar in this value.
+  if ((caseValue & ((__swift_uint64_t)(0x1) << 63)) == 0) {
+    auto distance = (__swift_int32_t)((caseValue << 1) >> 22);
+    auto mappedScalar = (__swift_uint32_t)((__swift_int32_t)(scalar) - distance);
+    
+    buffer[0] = mappedScalar;
+    return;
+  }
+  
+  // Our top bit WAS set which means this scalar maps to multiple scalars.
+  // Lookup our mapping in the full mph.
+  auto fullMphIdx = _swift_stdlib_getMphIdx(scalar, CASE_FULL_FOLD_LEVEL_COUNT,
+                                            _swift_stdlib_case_full_keys,
+                                            _swift_stdlib_case_full_ranks,
+                                            _swift_stdlib_case_full_sizes);
+  
+  auto fullCaseValue = _swift_stdlib_case_full[fullMphIdx];
+
+  // Count is either 2 or 3.
+  auto count = fullCaseValue >> 62;
+
+  for (__swift_uint64_t i = 0; i != count; i += 1) {
+    auto distance = (__swift_int32_t)(fullCaseValue & 0xFFFF);
+
+    if ((fullCaseValue & 0x10000) != 0) {
+      distance = -distance;
+    }
+
+    fullCaseValue >>= 17;
+
+    auto mappedScalar = (__swift_uint32_t)((__swift_int32_t)(scalar) - distance);
+
+    buffer[i] = mappedScalar;
+  }
+#endif
+}