[+] AuCodepointsDecodeOne

Include/auROXTL/auStringUtils.hpp

@@ -13,7 +13,7 @@
     Implements: AuStringContains, AuEndsWith, AuStartsWith, AuReplaceAll, AuSplitString (views), AuSplitStringLegacy (returns an array of strings instead of views)
                 AuToLower(char), AuToUpper(char), AuToLower(view), AuToUpper(view).
     Implements: AuCodepointsTransform, AuCodepointsTransformASCIIOp, AuCodepointsForEach, AuCodepointsToLower, AuCodepointsToUpper,
-                AuCodepointsCount, AuCodepointsNextLength, AuCodepointsDecode, AuCodepointsEncodeInto,
+                AuCodepointsCount, AuCodepointsNextLength, AuCodepointsDecodeOne, AuCodepointsDecode, AuCodepointsEncodeInto,
                 AuCodepointsGetByteOffset(CodepointOffset_t),AuCodepointsGetByteLength(CodepointOffset_t),
                 AuCodepointsFindByteOffset[Unsafe], AuCodepointsFindCodepointOffset(view, CodepointOffset_t), AuCodepointsFindCodepointOffset(CodepointByteOffset_t),
                 AuCodepointsContains,
@@ -171,7 +171,7 @@ static auline AuString AuCodepointsTransformASCIIOp(T op, const AuROString &in)
     return ret;
 }
 
-static auline CodepointOffset_t AuCodepointsCount(const AuROString &in)
+static auline constexpr CodepointOffset_t AuCodepointsCount(const AuROString &in)
 {
     CodepointOffset_t uCounter {};
     auto uLength = in.length();
@@ -253,7 +253,7 @@ static auline CodepointOffset_t AuCodepointsCount(const AuROString &in)
     return uCounter;
 }
 
-static auline CodepointByteOffset_t AuCodepointsNextLength(const AuROString &in)
+static auline constexpr CodepointByteOffset_t AuCodepointsNextLength(const AuROString &in)
 {
     if (in.length())
     {
@@ -316,17 +316,17 @@ static auline CodepointByteOffset_t AuCodepointsNextLength(const AuROString &in)
     return 0;
 }
 
-static auline bool AuIsAlpha(char c)
+static auline constexpr bool AuIsAlpha(char c)
 {
     return (c) && (((unsigned char)c | 0x20) - 'a' < 26);
 }
 
-static auline char AuToLower(char c)
+static auline constexpr char AuToLower(char c)
 {
     return AuIsAlpha(c) ? c | 0x20 : c;
 }
 
-static auline char AuToUpper(char c)
+static auline constexpr char AuToUpper(char c)
 {
     return AuIsAlpha(c) ? c & ~0x20 : c;
 }
@@ -351,6 +351,73 @@ static auline AuString AuToUpper(const AuROString &in)
     return AuCodepointsToUpper(in);
 }
 
+static constexpr AuOptional<AuUInt32> AuCodepointsDecodeOne(const AuROString &in)
+{
+    if (in.empty())
+    {
+        return {};
+    }
+
+    auto uLength = in.length();
+
+    const char *pItr = in.data();
+    const char *pEnd = pItr + uLength;
+
+    while (pItr < pEnd)
+    {
+        AuUInt32 c {};
+
+        if ((c = *pItr) <= 0x7FU)
+        {
+            ++pItr;
+        }
+        else
+        {
+            AuUInt32 nby {};
+
+            if ((*pItr & 0xC0U) != 0xC0U)
+            {
+                return {};
+            }
+
+            for (AuUInt8 b = *pItr; (b & 0x80U) != 0; b <<= 1, ++nby)
+            {
+            }
+
+            if (nby > kAuCodepointUTF8MaxBytes)
+            {
+            #if defined(AURORA_UTF8_I_SUCK_AND_WANT_MODERN_UTF8_WANT_THROW)
+                AU_THROW_CONST_STRING("Illegal UTF8");
+            #endif
+                return {};
+            }
+
+            if (AuUInt(pEnd - pItr) < AuUInt(nby))
+            {
+                return {};
+            }
+
+            c = *pItr & (AuUInt8(0xFFU) >> (nby + 1));
+
+            for (AuUInt32 i = 1; i < nby; ++i)
+            {
+                if ((pItr[i] & 0xC0U) != 0x80U)
+                {
+                    return {};
+                }
+
+                c = (c << 6) | (pItr[i] & 0x3FU);
+            }
+
+            pItr += nby;
+        }
+
+        return c;
+    }
+
+    return {};
+}
+
 static AuList<AuUInt32> AuCodepointsDecode(const AuROString &in)
 {
     AuList<AuUInt32> ret;
@@ -696,7 +763,7 @@ static bool AuCodepointsIsEqualIgnoreCase(const AuROString &inA,
     return true;
 }
 
-static auline CodepointByteOffset_t AuCodepointsGetByteOffset(const AuROString &in,
+static auline constexpr CodepointByteOffset_t AuCodepointsGetByteOffset(const AuROString &in,
                                                                         CodepointOffset_t uCodepointIndex)
 {
     AuUInt uCounter {};
@@ -785,7 +852,7 @@ static auline CodepointByteOffset_t AuCodepointsGetByteOffset(const AuROString &
     return AuROString::npos;
 }
 
-static auline CodepointByteOffset_t AuCodepointsGetByteLength(const AuROString &in,
+static auline constexpr CodepointByteOffset_t AuCodepointsGetByteLength(const AuROString &in,
                                                                         CodepointOffset_t uCodepointIndex)
 {
     AuUInt uCounter {};
@@ -1070,7 +1137,7 @@ static constexpr CodepointByteOffset_t AuCodepointsFindByteOffsetUnsafe(const Au
     return AuROString::npos;
 }
 
-static CodepointByteOffset_t AuCodepointsFindPreviousValidByteOffsetFromOffset(const AuROString &in,
+static constexpr CodepointByteOffset_t AuCodepointsFindPreviousValidByteOffsetFromOffset(const AuROString &in,
                                                                                          CodepointOffset_t uStartPosition = {})
 {      
     AuUInt uCounter    = 0;
@@ -1165,7 +1232,7 @@ static CodepointByteOffset_t AuCodepointsFindPreviousValidByteOffsetFromOffset(c
     return AuROString::npos;
 }
 
-static CodepointByteOffset_t AuCodepointsFindPreviousValidByteOffsetFromByteOffset(const AuROString &in,
+static constexpr CodepointByteOffset_t AuCodepointsFindPreviousValidByteOffsetFromByteOffset(const AuROString &in,
                                                                                              CodepointByteOffset_t uStartPosition = {})
 {      
     const char * pStart = in.data();
@@ -1202,7 +1269,7 @@ static CodepointByteOffset_t AuCodepointsFindPreviousValidByteOffsetFromByteOffs
     }
 }
 
-static CodepointOffset_t AuCodepointsFindCodepointOffset(const AuROString &in,
+static constexpr CodepointOffset_t AuCodepointsFindCodepointOffset(const AuROString &in,
                                                                    CodepointByteOffset_t uBytePosition)
 {
     return AuCodepointsCount(in.substr(0, uBytePosition));
@@ -1437,7 +1504,7 @@ static bool AuCodepointsEndsWithEqualIgnoreCase(const AuROString &inA,
     return true;
 }
 
-static AuUInt AuCodepointsReverseIterate(const AuROString &string)
+static constexpr AuUInt AuCodepointsReverseIterate(const AuROString &string)
 {
     auto uLastValid = AuCodepointsFindPreviousValidByteOffsetFromByteOffset(string, string.Size());
     if (uLastValid == AuROString::npos)
@@ -1448,7 +1515,7 @@ static AuUInt AuCodepointsReverseIterate(const AuROString &string)
     return string.Size() - uLastValid;
 }
 
-static AuROString AuCodepointsReverseIterateSubStrPrefixView(const AuROString &string)
+static constexpr AuROString AuCodepointsReverseIterateSubStrPrefixView(const AuROString &string)
 {
     auto uOffset = AuCodepointsReverseIterate(string);
     if (uOffset == AuROString::npos)
@@ -1459,7 +1526,7 @@ static AuROString AuCodepointsReverseIterateSubStrPrefixView(const AuROString &s
     return string.RemoveSuffix(uOffset);
 }
 
-static AuROString AuCodepointsReverseIterateSubStrSuffixView(const AuROString &string)
+static constexpr AuROString AuCodepointsReverseIterateSubStrSuffixView(const AuROString &string)
 {
     auto uLastValid = AuCodepointsFindPreviousValidByteOffsetFromByteOffset(string, string.Size());
     if (uLastValid == AuROString::npos)