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fb: implement assign in terms of a visitor.

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We'll reuse this visitor in the next commit.
This commit is contained in:
David Goldblatt 2020-12-02 11:46:49 -08:00 committed by David Goldblatt
parent 734e72ce8f
commit e6c057ad35
1 changed files with 32 additions and 23 deletions
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55
include/jemalloc/internal/flat_bitmap.h
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@ -71,21 +71,16 @@ fb_unset(fb_group_t *fb, size_t nbits, size_t bit) {
fb[group_ind] &= ~((fb_group_t)1 << bit_ind);
}
JEMALLOC_ALWAYS_INLINE void
fb_assign_group_impl(fb_group_t *fb, size_t start, size_t cnt, bool val) {
assert(cnt > 0);
assert(start + cnt - 1 < FB_GROUP_BITS);
fb_group_t bits = ((~(fb_group_t)0) >> (FB_GROUP_BITS - cnt)) << start;
if (val) {
*fb |= bits;
} else {
*fb &= ~bits;
}
}
/*
* Some implementation details. This visitation function lets us apply a group
* visitor to each group in the bitmap (potentially modifying it). The mask
* indicates which bits are logically part of the visitation.
*/
typedef void (*fb_group_visitor_t)(void *ctx, fb_group_t *fb, fb_group_t mask);
JEMALLOC_ALWAYS_INLINE void
fb_assign_impl(fb_group_t *fb, size_t nbits, size_t start, size_t cnt,
bool val) {
fb_visit_impl(fb_group_t *fb, size_t nbits, fb_group_visitor_t visit, void *ctx,
size_t start, size_t cnt) {
assert(start + cnt - 1 < nbits);
size_t group_ind = start / FB_GROUP_BITS;
size_t start_bit_ind = start % FB_GROUP_BITS;
@ -93,10 +88,8 @@ fb_assign_impl(fb_group_t *fb, size_t nbits, size_t start, size_t cnt,
* The first group is special; it's the only one we don't start writing
* to from bit 0.
*/
size_t first_group_cnt =
(start_bit_ind + cnt > FB_GROUP_BITS
? FB_GROUP_BITS - start_bit_ind
: cnt);
size_t first_group_cnt = (start_bit_ind + cnt > FB_GROUP_BITS
? FB_GROUP_BITS - start_bit_ind : cnt);
/*
* We can basically split affected words into:
* - The first group, where we touch only the high bits
@ -106,32 +99,48 @@ fb_assign_impl(fb_group_t *fb, size_t nbits, size_t start, size_t cnt,
* this can lead to bad codegen for those middle words.
*/
/* First group */
fb_assign_group_impl(&fb[group_ind], start_bit_ind, first_group_cnt,
val);
fb_group_t mask = ((~(fb_group_t)0)
>> (FB_GROUP_BITS - first_group_cnt))
<< start_bit_ind;
visit(ctx, &fb[group_ind], mask);
cnt -= first_group_cnt;
group_ind++;
/* Middle groups */
while (cnt > FB_GROUP_BITS) {
fb_assign_group_impl(&fb[group_ind], 0, FB_GROUP_BITS, val);
visit(ctx, &fb[group_ind], ~(fb_group_t)0);
cnt -= FB_GROUP_BITS;
group_ind++;
}
/* Last group */
if (cnt != 0) {
fb_assign_group_impl(&fb[group_ind], 0, cnt, val);
mask = (~(fb_group_t)0) >> (FB_GROUP_BITS - cnt);
visit(ctx, &fb[group_ind], mask);
}
}
JEMALLOC_ALWAYS_INLINE void
fb_assign_visitor(void *ctx, fb_group_t *fb, fb_group_t mask) {
bool val = *(bool *)ctx;
if (val) {
*fb |= mask;
} else {
*fb &= ~mask;
}
}
/* Sets the cnt bits starting at position start. Must not have a 0 count. */
static inline void
fb_set_range(fb_group_t *fb, size_t nbits, size_t start, size_t cnt) {
fb_assign_impl(fb, nbits, start, cnt, true);
bool val = true;
fb_visit_impl(fb, nbits, &fb_assign_visitor, &val, start, cnt);
}
/* Unsets the cnt bits starting at position start. Must not have a 0 count. */
static inline void
fb_unset_range(fb_group_t *fb, size_t nbits, size_t start, size_t cnt) {
fb_assign_impl(fb, nbits, start, cnt, false);
bool val = false;
fb_visit_impl(fb, nbits, &fb_assign_visitor, &val, start, cnt);
}
/*