1 files changed, 87 insertions, 0 deletions
diff --git a/src/utf.cc b/src/utf.cc
new file mode 100644
index 0000000..208dd33
--- /dev/null
+++ b/src/utf.cc
@@ -0,0 +1,87 @@
+// -*- mode: c++; c-basic-offset: 2; -*-
+
+#include "common.hh"
+
+#include <string.h>
+
+#include "utf.hh"
+
+char* read_utf8(char const* in, size_t max, uint32_t* out) {
+  if (!in) return nullptr;
+  if (max == 0) return const_cast<char*>(in);
+  auto d = reinterpret_cast<uint8_t*>(const_cast<char*>(in));
+  switch (*d >> 4) {
+  case 0:
+    if (*d == 0) {
+      if (out) *out = 0;
+      break;
+    }
+    // Fallthrough
+  default:
+    if (out) *out = *d;
+    ++d;
+    break;
+  case 12:
+  case 13: {
+    if (max < 2) return nullptr;
+    if ((d[1] & 0xc0) != 0x80) return nullptr;
+    uint32_t tmp = (d[0] & 0x1f) << 6 | (d[1] & 0x3f);
+    if (tmp < 0x80) return nullptr;
+    if (out) *out = tmp;
+    d += 2;
+    break;
+  }
+  case 14: {
+    if (max < 3) return nullptr;
+    if ((d[1] & 0xc0) != 0x80) return nullptr;
+    if ((d[2] & 0xc0) != 0x80) return nullptr;
+    uint32_t tmp = (d[0] & 0xf) << 12 | (d[1] & 0x3f) << 6 | (d[2] & 0x3f);
+    if (tmp < 0x800) return nullptr;
+    if (out) *out = tmp;
+    d += 3;
+    break;
+  }
+  case 15: {
+    if (max < 4) return nullptr;
+    if ((d[1] & 0xc0) != 0x80) return nullptr;
+    if ((d[2] & 0xc0) != 0x80) return nullptr;
+    if ((d[3] & 0xc0) != 0x80) return nullptr;
+    uint32_t tmp = (d[0] & 0x7) << 18 | (d[1] & 0x3f) << 12
+      | (d[2] & 0x3f) << 6 | (d[3] & 0x3f);
+    if (tmp < 0x10000) return nullptr;
+    if (out) *out = tmp;
+    d += 4;
+    break;
+  }
+  }
+  return reinterpret_cast<char*>(d);
+}
+
+bool valid_utf8(std::string const& str, size_t start, size_t len) {
+  if (start == 0) return valid_utf8(str.data(), std::min(str.size(), len));
+  if (start > str.size()) start = str.size();
+  if (len == std::string::npos || start + len > str.size()) {
+    len = str.size() - start;
+  }
+  return valid_utf8(str.data() + start, len);
+}
+
+bool valid_utf8(char const* str, size_t len) {
+  if (len == 0) return true;
+  if (!str) {
+    assert(false);
+    return false;
+  }
+  if (len == std::string::npos) {
+    len = strlen(str);
+    if (len == 0) return true;
+  }
+  auto end = str + len;
+  while (str < end) {
+    auto next = read_utf8(str, end - str, nullptr);
+    if (!next) return false;
+    if (next == str) return false;  // \0 are unexpected here
+    str = next;
+  }
+  return true;
+}