ha: Improve distribution of pool addresses over segments

This is particularly important for higher number of segments, but even
with small numbers there is a significant difference.  For instance,
with 4 segments the fourth segment had no IPs assigned with the old
code, no matter how large the pool, because none of the eight bits used
for the segment check hashed/mapped to it.

Author: tobiasbrunner

src/libcharon/plugins/ha/ha_attribute.c

@@ -159,13 +159,13 @@ static pool_t* get_pool(private_ha_attribute_t *this, char *name)
 }
 
 /**
- * Check if we are responsible for a bit in our bitmask
+ * Check if we are responsible for an offset
  */
-static bool responsible_for(private_ha_attribute_t *this, int bit)
+static bool responsible_for(private_ha_attribute_t *this, int offset)
 {
 	u_int segment;
 
-	segment = this->kernel->get_segment_int(this->kernel, bit);
+	segment = this->kernel->get_segment_int(this->kernel, offset);
 	return this->segments->is_active(this->segments, segment);
 }
 
@@ -175,7 +175,7 @@ METHOD(attribute_provider_t, acquire_address, host_t*,
 {
 	enumerator_t *enumerator;
 	pool_t *pool = NULL;
-	int offset = -1, byte, bit;
+	int offset = -1, tmp_offset, byte, bit;
 	host_t *address;
 	char *name;
 
@@ -199,10 +199,11 @@ METHOD(attribute_provider_t, acquire_address, host_t*,
 			{
 				for (bit = 0; bit < 8; bit++)
 				{
+					tmp_offset = byte * 8 + bit;
 					if (!(pool->mask[byte] & 1 << bit) &&
-						responsible_for(this, bit))
+						responsible_for(this, tmp_offset))
 					{
-						offset = byte * 8 + bit;
+						offset = tmp_offset;
 						pool->mask[byte] |= 1 << bit;
 						break;
 					}