Re: [Qemu-devel] [RFC] find_next_bit optimizations

[Peter Lieven]

> How would that be different in your patch?  But you can solve it by
> making two >= loops, one checking for 4*BITS_PER_LONG and one checking
> BITS_PER_LONG.
This is what I have now:

diff --git a/util/bitops.c b/util/bitops.c
index e72237a..b0dc93f 100644
--- a/util/bitops.c
+++ b/util/bitops.c
@@ -24,12 +24,13 @@ unsigned long find_next_bit(const unsigned long *addr, 
unsigned long size,
     const unsigned long *p = addr + BITOP_WORD(offset);
     unsigned long result = offset & ~(BITS_PER_LONG-1);
     unsigned long tmp;
+    unsigned long d0,d1,d2,d3;
 
     if (offset >= size) {
         return size;
     }
     size -= result;
-    offset %= BITS_PER_LONG;
+    offset &= (BITS_PER_LONG-1);
     if (offset) {
         tmp = *(p++);
         tmp &= (~0UL << offset);
@@ -42,7 +43,19 @@ unsigned long find_next_bit(const unsigned long *addr, 
unsigned long size,
         size -= BITS_PER_LONG;
         result += BITS_PER_LONG;
     }
-    while (size & ~(BITS_PER_LONG-1)) {
+    while (size >= 4*BITS_PER_LONG) {
+        d0 = *p;
+        d1 = *(p+1);
+        d2 = *(p+2);
+        d3 = *(p+3);
+        if (d0 || d1 || d2 || d3) {
+            break;
+        }
+        p+=4;
+        result += 4*BITS_PER_LONG;
+        size -= 4*BITS_PER_LONG;
+    }
+    while (size >= BITS_PER_LONG) {
         if ((tmp = *(p++))) {
             goto found_middle;
         }