bitmap_*() should cope with zero size bitmaps

... to match expectations set by memset()/memcpy().

Similarly for find_{first,next}_{,zero_}_bit() on x86.

__bitmap_shift_{left,right}() would also need fixing (they more
generally can't cope with the shift count being larger than the bitmap
size, and they perform undefined operations by possibly shifting an
unsigned long value by BITS_PER_LONG bits), but since these functions
aren't really used anywhere I wonder if we wouldn't better simply get
rid of them.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>

1 files changed, 64 insertions, 64 deletions

diff --git a/xen/include/xen/bitmap.h b/xen/include/xen/bitmap.h
index 56fe602adf..b5ec455ff4 100644
--- a/xen/include/xen/bitmap.h
+++ b/xen/include/xen/bitmap.h
@@ -108,123 +108,122 @@ extern int bitmap_allocate_region(unsigned long *bitmap, int pos, int order);
 		(1UL<<((nbits) % BITS_PER_LONG))-1 : ~0UL		\
 )
 
+#define bitmap_bytes(nbits) (BITS_TO_LONGS(nbits) * sizeof(unsigned long))
+
+#define bitmap_switch(nbits, zero_ret, small, large)			\
+	switch (-!__builtin_constant_p(nbits) | (nbits)) {		\
+	case 0:	return zero_ret;					\
+	case 1 ... BITS_PER_LONG:					\
+		small; break;						\
+	default:							\
+		large; break;						\
+	}
+
 static inline void bitmap_zero(unsigned long *dst, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		*dst = 0UL;
-	else {
-		int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
-		memset(dst, 0, len);
-	}
+	bitmap_switch(nbits,,
+		*dst = 0UL,
+		memset(dst, 0, bitmap_bytes(nbits)));
 }
 
 static inline void bitmap_fill(unsigned long *dst, int nbits)
 {
 	size_t nlongs = BITS_TO_LONGS(nbits);
-	if (nlongs > 1) {
-		int len = (nlongs - 1) * sizeof(unsigned long);
-		memset(dst, 0xff,  len);
+
+	switch (nlongs) {
+	default:
+		memset(dst, -1, (nlongs - 1) * sizeof(unsigned long));
+		/* fall through */
+	case 1:
+		dst[nlongs - 1] = BITMAP_LAST_WORD_MASK(nbits);
+		break;
 	}
-	dst[nlongs - 1] = BITMAP_LAST_WORD_MASK(nbits);
 }
 
 static inline void bitmap_copy(unsigned long *dst, const unsigned long *src,
 			int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		*dst = *src;
-	else {
-		int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
-		memcpy(dst, src, len);
-	}
+	bitmap_switch(nbits,,
+		*dst = *src,
+		memcpy(dst, src, bitmap_bytes(nbits)));
 }
 
 static inline void bitmap_and(unsigned long *dst, const unsigned long *src1,
 			const unsigned long *src2, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		*dst = *src1 & *src2;
-	else
-		__bitmap_and(dst, src1, src2, nbits);
+	bitmap_switch(nbits,,
+		*dst = *src1 & *src2,
+		__bitmap_and(dst, src1, src2, nbits));
 }
 
 static inline void bitmap_or(unsigned long *dst, const unsigned long *src1,
 			const unsigned long *src2, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		*dst = *src1 | *src2;
-	else
-		__bitmap_or(dst, src1, src2, nbits);
+	bitmap_switch(nbits,,
+		*dst = *src1 | *src2,
+		__bitmap_or(dst, src1, src2, nbits));
 }
 
 static inline void bitmap_xor(unsigned long *dst, const unsigned long *src1,
 			const unsigned long *src2, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		*dst = *src1 ^ *src2;
-	else
-		__bitmap_xor(dst, src1, src2, nbits);
+	bitmap_switch(nbits,,
+		*dst = *src1 ^ *src2,
+		__bitmap_xor(dst, src1, src2, nbits));
 }
 
 static inline void bitmap_andnot(unsigned long *dst, const unsigned long *src1,
 			const unsigned long *src2, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		*dst = *src1 & ~(*src2);
-	else
-		__bitmap_andnot(dst, src1, src2, nbits);
+	bitmap_switch(nbits,,
+		*dst = *src1 & ~*src2,
+		__bitmap_andnot(dst, src1, src2, nbits));
 }
 
 static inline void bitmap_complement(unsigned long *dst, const unsigned long *src,
 			int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		*dst = ~(*src) & BITMAP_LAST_WORD_MASK(nbits);
-	else
-		__bitmap_complement(dst, src, nbits);
+	bitmap_switch(nbits,,
+		*dst = ~*src & BITMAP_LAST_WORD_MASK(nbits),
+		__bitmap_complement(dst, src, nbits));
 }
 
 static inline int bitmap_equal(const unsigned long *src1,
 			const unsigned long *src2, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		return ! ((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits));
-	else
-		return __bitmap_equal(src1, src2, nbits);
+	bitmap_switch(nbits, -1,
+		return !((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)),
+		return __bitmap_equal(src1, src2, nbits));
 }
 
 static inline int bitmap_intersects(const unsigned long *src1,
 			const unsigned long *src2, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		return ((*src1 & *src2) & BITMAP_LAST_WORD_MASK(nbits)) != 0;
-	else
-		return __bitmap_intersects(src1, src2, nbits);
+	bitmap_switch(nbits, -1,
+		return ((*src1 & *src2) & BITMAP_LAST_WORD_MASK(nbits)) != 0,
+		return __bitmap_intersects(src1, src2, nbits));
 }
 
 static inline int bitmap_subset(const unsigned long *src1,
 			const unsigned long *src2, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		return ! ((*src1 & ~(*src2)) & BITMAP_LAST_WORD_MASK(nbits));
-	else
-		return __bitmap_subset(src1, src2, nbits);
+	bitmap_switch(nbits, -1,
+		return !((*src1 & ~*src2) & BITMAP_LAST_WORD_MASK(nbits)),
+		return __bitmap_subset(src1, src2, nbits));
 }
 
 static inline int bitmap_empty(const unsigned long *src, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		return ! (*src & BITMAP_LAST_WORD_MASK(nbits));
-	else
-		return __bitmap_empty(src, nbits);
+	bitmap_switch(nbits, -1,
+		return !(*src & BITMAP_LAST_WORD_MASK(nbits)),
+		return __bitmap_empty(src, nbits));
 }
 
 static inline int bitmap_full(const unsigned long *src, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		return ! (~(*src) & BITMAP_LAST_WORD_MASK(nbits));
-	else
-		return __bitmap_full(src, nbits);
+	bitmap_switch(nbits, -1,
+		return !(~*src & BITMAP_LAST_WORD_MASK(nbits)),
+		return __bitmap_full(src, nbits));
 }
 
 static inline int bitmap_weight(const unsigned long *src, int nbits)
@@ -235,21 +234,22 @@ static inline int bitmap_weight(const unsigned long *src, int nbits)
 static inline void bitmap_shift_right(unsigned long *dst,
 			const unsigned long *src, int n, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		*dst = *src >> n;
-	else
-		__bitmap_shift_right(dst, src, n, nbits);
+	bitmap_switch(nbits,,
+		*dst = *src >> n,
+		__bitmap_shift_right(dst, src, n, nbits));
 }
 
 static inline void bitmap_shift_left(unsigned long *dst,
 			const unsigned long *src, int n, int nbits)
 {
-	if (nbits <= BITS_PER_LONG)
-		*dst = (*src << n) & BITMAP_LAST_WORD_MASK(nbits);
-	else
-		__bitmap_shift_left(dst, src, n, nbits);
+	bitmap_switch(nbits,,
+		*dst = (*src << n) & BITMAP_LAST_WORD_MASK(nbits),
+		__bitmap_shift_left(dst, src, n, nbits));
 }
 
+#undef bitmap_switch
+#undef bitmap_bytes
+
 void bitmap_long_to_byte(uint8_t *bp, const unsigned long *lp, int nbits);
 void bitmap_byte_to_long(unsigned long *lp, const uint8_t *bp, int nbits);