[PATCH userspace] libsepol: cache ebitmap cardinality value

[Ondrej Mosnacek <omosnace@xxxxxxxxxx>]

According to profiling of semodule -BN, ebitmap_cardinality() is called
quite often and contributes a lot to the total runtime. Cache its result
in the ebitmap struct to reduce this overhead. The cached value is
invalidated on most modifying operations, but ebitmap_cardinality() is
usually called once the ebitmap doesn't change any more.

After this patch, the time to do 'semodule -BN' on Fedora Rawhide has
decreased from ~21.4s to ~18.6s (2.8s saved).

Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
---
 libsepol/include/sepol/policydb/ebitmap.h |  1 +
 libsepol/src/ebitmap.c                    | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/libsepol/include/sepol/policydb/ebitmap.h b/libsepol/include/sepol/policydb/ebitmap.h
index e62df01c..53fafdaa 100644
--- a/libsepol/include/sepol/policydb/ebitmap.h
+++ b/libsepol/include/sepol/policydb/ebitmap.h
@@ -37,6 +37,7 @@ typedef struct ebitmap_node {
 typedef struct ebitmap {
 	ebitmap_node_t *node;	/* first node in the bitmap */
 	uint32_t highbit;	/* highest position in the total bitmap */
+	unsigned int cardinality;	/* cached value of cardinality */
 } ebitmap_t;
 
 #define ebitmap_length(e) ((e)->highbit)
diff --git a/libsepol/src/ebitmap.c b/libsepol/src/ebitmap.c
index 6c9951b7..d23444ce 100644
--- a/libsepol/src/ebitmap.c
+++ b/libsepol/src/ebitmap.c
@@ -67,6 +67,7 @@ int ebitmap_union(ebitmap_t * dst, const ebitmap_t * e1)
 	ebitmap_destroy(dst);
 	dst->node = tmp.node;
 	dst->highbit = tmp.highbit;
+	dst->cardinality = 0;
 
 	return 0;
 }
@@ -128,9 +129,14 @@ int ebitmap_andnot(ebitmap_t *dst, ebitmap_t *e1, ebitmap_t *e2, unsigned int ma
 unsigned int ebitmap_cardinality(ebitmap_t *e1)
 {
 	unsigned int i, count = 0;
+
+	if (e1->cardinality || e1->highbit == 0)
+		return e1->cardinality;
+
 	for (i=ebitmap_startbit(e1); i < ebitmap_length(e1); i++)
 		if (ebitmap_get_bit(e1, i))
 			count++;
+	e1->cardinality = count;
 	return count;
 }
 
@@ -194,6 +200,7 @@ int ebitmap_cpy(ebitmap_t * dst, const ebitmap_t * src)
 	}
 
 	dst->highbit = src->highbit;
+	dst->cardinality = src->cardinality;
 	return 0;
 }
 
@@ -309,6 +316,7 @@ int ebitmap_set_bit(ebitmap_t * e, unsigned int bit, int value)
 					free(n);
 				}
 			}
+			e->cardinality = 0; /* invalidate cached cardinality */
 			return 0;
 		}
 		prev = n;
@@ -339,6 +347,7 @@ int ebitmap_set_bit(ebitmap_t * e, unsigned int bit, int value)
 		e->node = new;
 	}
 
+	e->cardinality = 0; /* invalidate cached cardinality */
 	return 0;
 }
 
@@ -358,6 +367,7 @@ void ebitmap_destroy(ebitmap_t * e)
 
 	e->highbit = 0;
 	e->node = 0;
+	e->cardinality = 0;
 	return;
 }
 
-- 
2.24.1