1 files changed, 86 insertions, 0 deletions
diff --git a/euler/source/std/string.cpp b/euler/source/std/string.cpp
new file mode 100644
index 0000000..31c47a5
--- /dev/null
+++ b/euler/source/std/string.cpp
@@ -0,0 +1,86 @@
+#include <cctype>
+#include <string>
+
+namespace std {
+
+  int stoi(const std::string &str, size_t *pos, int base) {
+    //TODO: exceptions
+
+    size_t i = 0;
+    while (isspace(str[i]))
+      ++i;
+
+    bool is_negative = false;
+    if (str[i] == '-') {
+      is_negative = true;
+      ++i;
+    }
+    else if (str[i] == '+')
+      ++i;
+
+    if ((base == 16 || base == 0) && str[i] == '0' &&
+        (str[i + 1] == 'x' || str[i + 1] == 'X')) {
+      base = 16;
+      i += 2;
+    }
+
+    else if ((base == 8 || base == 0) && str[i] == '0') {
+      base = 8;
+      ++i;
+    }
+
+    else if (base == 0)
+      base = 10;
+
+    int value = 0;
+
+    while (true) {
+      char c = str[i];
+      if (c >= '0' && c < '0' + base)
+        value = value * base + c - '0';
+      else if (c >= 'a' && c < 'a' + base - 10)
+        value = value * base + c - 'a' + 10;
+      else if (c >= 'A' && c < 'A' + base - 10)
+        value = value * base + c - 'A' + 10;
+      else
+        break;
+    }
+
+    if (pos != 0)
+      *pos = i;
+
+    return is_negative ? -value : value;
+
+  }
+
+  std::string to_string(int value) {
+
+    int max_place = 1;
+    int places = 1;
+    while (max_place <= value / 10) {
+      max_place *= 10;
+      ++places;
+    }
+
+    std::string s;
+    s.resize(places);
+
+    for (int i = 0; i < places; ++i) {
+      s[i] = (value / max_place) % 10 + '0';
+      max_place /= 10;
+    }
+
+    return s;
+
+  }
+
+  std::string operator +(std::string &&lhs, std::string &&rhs) {
+    std::string s = std::move(lhs);
+    s.resize(lhs.size() + rhs.size());
+    for (size_t i = 0; i < rhs.size(); ++i)
+      s[lhs.size() + i] = rhs[i];
+    rhs.clear();
+    return s;
+  }
+
+}