From 22d55029c262cbb127d96a78b27792dc78d2c99d Mon Sep 17 00:00:00 2001
From: "Frank J. T. Wojcik" <fwojcik@uw.edu>
Date: Thu, 3 Aug 2023 20:19:09 -0700
Subject: [PATCH] Speed up Blob highzerobits implementation

---
 util/Blob.cpp | 20 +-------------------
 util/Blob.h   | 36 ++++++++++++++++++++++++++++++------
 2 files changed, 31 insertions(+), 25 deletions(-)

diff --git a/util/Blob.cpp b/util/Blob.cpp
index 47c1b7b5..6d02d640 100644
--- a/util/Blob.cpp
+++ b/util/Blob.cpp
@@ -21,22 +21,4 @@
 #include "Blob.h"
 
 //-----------------------------------------------------------------------------
-// For highzerobits()
-const uint8_t hzb[256] = {
-    8, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
-    3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
-    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
-    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
-    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-};
+// Someday this will have Blob unit tests
diff --git a/util/Blob.h b/util/Blob.h
index 820f7a7f..1420742c 100644
--- a/util/Blob.h
+++ b/util/Blob.h
@@ -47,8 +47,6 @@
  */
 #include <algorithm>
 
-extern const uint8_t hzb[256];
-
 //-----------------------------------------------------------------------------
 #define _bytes ((size_t)(_bits + 7) / 8)
 template <unsigned _bits>
@@ -283,13 +281,39 @@ class Blob {
 
     static FORCE_INLINE uint32_t _highzerobits( const uint8_t * bytes, const size_t len ) {
         uint32_t zb = 0;
+        size_t i = _bytes;
 
-        for (ssize_t i = len - 1; i >= 0; i--) {
-            zb += hzb[bytes[i]];
-            if (bytes[i] != 0) {
-                break;
+        while (i >= 8) {
+            uint64_t a;
+            i -= 8;
+            memcpy(&a, &bytes[i], 8); a = COND_BSWAP(a, isBE());
+            if (a != 0) {
+                zb += clz8(a);
+                return zb;
             }
+            zb += 64;
         }
+        while (i >= 4) {
+            uint32_t a;
+            i -= 4;
+            memcpy(&a, &bytes[i], 4); a = COND_BSWAP(a, isBE());
+            if (a != 0) {
+                zb += clz4(a);
+                return zb;
+            }
+            zb += 32;
+        }
+        while (i >= 1) {
+            uint32_t a;
+            i -= 1;
+            a = bytes[i];
+            if (a != 0) {
+                zb += clz4(a);
+                return zb;
+            }
+            zb += 8;
+        }
+
         return zb;
     }