From bca569ae535e4fb7a38f9ec9514e667fc15a29d2 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 21 Nov 2022 23:19:42 -0700
Subject: [PATCH] [array] Speed up hash() for byte arrays

---
 src/hb-array.hh | 32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/src/hb-array.hh b/src/hb-array.hh
index fbc98e7c7..562f03cdf 100644
--- a/src/hb-array.hh
+++ b/src/hb-array.hh
@@ -424,17 +424,41 @@ inline bool hb_array_t<const unsigned char>::operator == (const hb_array_t<const
   return 0 == hb_memcmp (arrayZ, o.arrayZ, length);
 }
 
+
+/* Specialize hash() for byte arrays. */
+
 template <>
-inline uint32_t hb_array_t<const char>::hash () const {
+inline uint32_t hb_array_t<const char>::hash () const
+{
   uint32_t current = 0;
-  for (unsigned int i = 0; i < this->length; i++)
+  unsigned i = 0;
+
+#if defined(__OPTIMIZE__) && !defined(HB_NO_PACKED) && \
+    ((defined(__GNUC__) && __GNUC__ >= 5) || defined(__clang__))
+  struct __attribute__((packed)) packed_uint32_t { uint32_t v; };
+  for (; i + 4 <= this->length; i += 4)
+    current = current * 31 + (uint32_t) ((((packed_uint32_t *) &this->arrayZ[i])->v) * 2654435761u);
+#endif
+
+  for (; i < this->length; i++)
     current = current * 31 + (uint32_t) (this->arrayZ[i] * 2654435761u);
   return current;
 }
+
 template <>
-inline uint32_t hb_array_t<const unsigned char>::hash () const {
+inline uint32_t hb_array_t<const unsigned char>::hash () const
+{
   uint32_t current = 0;
-  for (unsigned int i = 0; i < this->length; i++)
+  unsigned i = 0;
+
+#if defined(__OPTIMIZE__) && !defined(HB_NO_PACKED) && \
+    ((defined(__GNUC__) && __GNUC__ >= 5) || defined(__clang__))
+  struct __attribute__((packed)) packed_uint32_t { uint32_t v; };
+  for (; i + 4 <= this->length; i += 4)
+    current = current * 31 + (uint32_t) ((((packed_uint32_t *) &this->arrayZ[i])->v) * 2654435761u);
+#endif
+
+  for (; i < this->length; i++)
     current = current * 31 + (uint32_t) (this->arrayZ[i] * 2654435761u);
   return current;
 }