Functions added: FindLongestCommonSuffix, FindLongestCommonPrefix.

PiperOrigin-RevId: 539784770
Change-Id: Ie224afa04af023bbddc89b967e8c8440f9e8a887

1 files changed, 66 insertions, 1 deletions

diff --git a/absl/strings/match.cc b/absl/strings/match.cc
index b65cbc67..3b81b2c0 100644
--- a/absl/strings/match.cc
+++ b/absl/strings/match.cc
@@ -13,8 +13,13 @@
 // limitations under the License.
 
 #include "absl/strings/match.h"
-#include "absl/strings/ascii.h"
 
+#include <algorithm>
+#include <cstdint>
+
+#include "absl/base/internal/endian.h"
+#include "absl/numeric/bits.h"
+#include "absl/strings/ascii.h"
 #include "absl/strings/internal/memutil.h"
 
 namespace absl {
@@ -61,5 +66,65 @@ bool EndsWithIgnoreCase(absl::string_view text,
          EqualsIgnoreCase(text.substr(text.size() - suffix.size()), suffix);
 }
 
+absl::string_view FindLongestCommonPrefix(absl::string_view a,
+                                          absl::string_view b) {
+  const absl::string_view::size_type limit = std::min(a.size(), b.size());
+  const char* const pa = a.data();
+  const char* const pb = b.data();
+  absl::string_view::size_type count = (unsigned) 0;
+
+  if (ABSL_PREDICT_FALSE(limit < 8)) {
+    while (ABSL_PREDICT_TRUE(count + 2 <= limit)) {
+      uint16_t xor_bytes = absl::little_endian::Load16(pa + count) ^
+                           absl::little_endian::Load16(pb + count);
+      if (ABSL_PREDICT_FALSE(xor_bytes != 0)) {
+        if (ABSL_PREDICT_TRUE((xor_bytes & 0xff) == 0)) ++count;
+        return absl::string_view(pa, count);
+      }
+      count += 2;
+    }
+    if (ABSL_PREDICT_TRUE(count != limit)) {
+      if (ABSL_PREDICT_TRUE(pa[count] == pb[count])) ++count;
+    }
+    return absl::string_view(pa, count);
+  }
+
+  do {
+    uint64_t xor_bytes = absl::little_endian::Load64(pa + count) ^
+                         absl::little_endian::Load64(pb + count);
+    if (ABSL_PREDICT_FALSE(xor_bytes != 0)) {
+      count += static_cast<uint64_t>(absl::countr_zero(xor_bytes) >> 3);
+      return absl::string_view(pa, count);
+    }
+    count += 8;
+  } while (ABSL_PREDICT_TRUE(count + 8 < limit));
+
+  count = limit - 8;
+  uint64_t xor_bytes = absl::little_endian::Load64(pa + count) ^
+                       absl::little_endian::Load64(pb + count);
+  if (ABSL_PREDICT_TRUE(xor_bytes != 0)) {
+    count += static_cast<uint64_t>(absl::countr_zero(xor_bytes) >> 3);
+    return absl::string_view(pa, count);
+  }
+  return absl::string_view(pa, limit);
+}
+
+absl::string_view FindLongestCommonSuffix(absl::string_view a,
+                                          absl::string_view b) {
+  const absl::string_view::size_type limit = std::min(a.size(), b.size());
+  if (limit == 0) return absl::string_view();
+
+  const char* pa = a.data() + a.size() - 1;
+  const char* pb = b.data() + b.size() - 1;
+  absl::string_view::size_type count = (unsigned) 0;
+  while (count < limit && *pa == *pb) {
+    --pa;
+    --pb;
+    ++count;
+  }
+
+  return absl::string_view(++pa, count);
+}
+
 ABSL_NAMESPACE_END
 }  // namespace absl