Make StartsWith and EndsWith constexpr.

This required rewriting StartsWith and EndsWith to not use memcmp and just create a string_view for the substring instead which can then be compared with operator==.

PiperOrigin-RevId: 702095989
Change-Id: I73474dd2e9a7fbbde563baf39e7cedd4fc2357e7

absl/strings/match.h

@@ -55,22 +55,32 @@ inline bool StrContains(absl::string_view haystack, char needle) noexcept {
 // StartsWith()
 //
 // Returns whether a given string `text` begins with `prefix`.
-inline bool StartsWith(absl::string_view text,
-                       absl::string_view prefix) noexcept {
-  return prefix.empty() ||
-         (text.size() >= prefix.size() &&
-          memcmp(text.data(), prefix.data(), prefix.size()) == 0);
+inline constexpr bool StartsWith(absl::string_view text,
+                                 absl::string_view prefix) noexcept {
+  if (prefix.empty()) {
+    return true;
+  }
+  if (text.size() < prefix.size()) {
+    return false;
+  }
+  absl::string_view possible_match = text.substr(0, prefix.size());
+
+  return possible_match == prefix;
 }
 
 // EndsWith()
 //
 // Returns whether a given string `text` ends with `suffix`.
-inline bool EndsWith(absl::string_view text,
-                     absl::string_view suffix) noexcept {
-  return suffix.empty() ||
-         (text.size() >= suffix.size() &&
-          memcmp(text.data() + (text.size() - suffix.size()), suffix.data(),
-                 suffix.size()) == 0);
+inline constexpr bool EndsWith(absl::string_view text,
+                               absl::string_view suffix) noexcept {
+  if (suffix.empty()) {
+    return true;
+  }
+  if (text.size() < suffix.size()) {
+    return false;
+  }
+  absl::string_view possible_match = text.substr(text.size() - suffix.size());
+  return possible_match == suffix;
 }
 // StrContainsIgnoreCase()
 //