convenience features (#21)

core/src/util/SetNoNatural.cpp

@@ -0,0 +1,69 @@
+#include "ccm/util/SetNoNatural.hpp"
+
+#include <cctype>
+
+namespace ccm {
+
+namespace {
+
+[[nodiscard]] bool isAsciiDigit(char c) noexcept {
+    return std::isdigit(static_cast<unsigned char>(c)) != 0;
+}
+
+[[nodiscard]] int cmpChar(char a, char b) noexcept {
+    const auto ua = static_cast<unsigned char>(a);
+    const auto ub = static_cast<unsigned char>(b);
+    if (ua < ub) return -1;
+    if (ua > ub) return 1;
+    return 0;
+}
+
+}  // namespace
+
+int compareSetNoNatural(std::string_view a, std::string_view b) noexcept {
+    std::size_t i = 0;
+    std::size_t j = 0;
+
+    while (i < a.size() && j < b.size()) {
+        const bool aDigit = isAsciiDigit(a[i]);
+        const bool bDigit = isAsciiDigit(b[j]);
+
+        if (aDigit && bDigit) {
+            std::size_t aEnd = i;
+            while (aEnd < a.size() && isAsciiDigit(a[aEnd])) ++aEnd;
+            std::size_t bEnd = j;
+            while (bEnd < b.size() && isAsciiDigit(b[bEnd])) ++bEnd;
+
+            std::size_t aSig = i;
+            while (aSig < aEnd && a[aSig] == '0') ++aSig;
+            std::size_t bSig = j;
+            while (bSig < bEnd && b[bSig] == '0') ++bSig;
+
+            const std::size_t aLen = aEnd - aSig;
+            const std::size_t bLen = bEnd - bSig;
+            if (aLen != bLen) return aLen < bLen ? -1 : 1;
+
+            for (std::size_t k = 0; k < aLen; ++k) {
+                const int c = cmpChar(a[aSig + k], b[bSig + k]);
+                if (c != 0) return c;
+            }
+
+            i = aEnd;
+            j = bEnd;
+            continue;
+        }
+
+        const int c = cmpChar(a[i], b[j]);
+        if (c != 0) return c;
+        ++i;
+        ++j;
+    }
+
+    if (i == a.size() && j == b.size()) {
+        if (a == b) return 0;
+        return a < b ? -1 : 1;
+    }
+    return i == a.size() ? -1 : 1;
+}
+
+}  // namespace ccm