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Make __demangle() heap 10% more compact

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Justine Tunney 2024-06-02 16:09:00 -07:00
parent 2ca491dc56
commit b003888696
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GPG key ID: BE714B4575D6E328
1 changed files with 16 additions and 8 deletions
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24
libc/intrin/demangle.c
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@ -68,11 +68,11 @@ Copyright (c) 2024 Justine Tunney <jtunney@gmail.com>");
* and 100% lockless, and uses absolutely no writable static memory. * and 100% lockless, and uses absolutely no writable static memory.
* That makes it also great for kernel and embedded development. * That makes it also great for kernel and embedded development.
* *
* - We made it go 3x faster. It's almost as fast as libcxxabi now. The * - We made it go 2x faster. It's almost as fast as libcxxabi now. The
* lightweight Dennis Ritchie style demangle_malloc() implementation * lightweight Dennis Ritchie style demangle_malloc() implementation
* helped. What also helped is introducing stack_str and strlcpy(). * helped. What also helped is introducing stack_str and strlcpy().
* *
* - We made it use 4x less memory. This came with the tradeoff of * - We made it use 3x less memory. This came with the tradeoff of
* imposing limitations similar to embedded software. Rather than * imposing limitations similar to embedded software. Rather than
* using pointers, we use 16-bit indexes into a heap that can grow no * using pointers, we use 16-bit indexes into a heap that can grow no
* larger than 64kb. Please note that a buffer size of 20kb is more * larger than 64kb. Please note that a buffer size of 20kb is more
@ -383,7 +383,7 @@ static privileged returnspointerwithnoaliases returnsnonnull void *
demangle_malloc(struct demangle_data *h, int a, int n) demangle_malloc(struct demangle_data *h, int a, int n)
{ {
uintptr_t ptr; uintptr_t ptr;
int next, next2; int rem, next, next2;
index_t *link, *link2; index_t *link, *link2;
int b = sizeof(index_t); int b = sizeof(index_t);
@ -397,12 +397,20 @@ demangle_malloc(struct demangle_data *h, int a, int n)
next = h->free; next = h->free;
link = &h->free; link = &h->free;
while (next) { while (next) {
next2 = *(index_t *)(h->heap + next);
link2 = (index_t *)(h->heap + next); link2 = (index_t *)(h->heap + next);
if (!(next & (a - 1)) && next2 = *link2;
n <= ((index_t *)(h->heap + next))[-1]) { if (!(next & (a - 1)) && (rem = link2[-1] - n) >= 0) {
*link = next2; if (rem < (b << 1)) {
return (void *)(h->heap + next); *link = next2;
} else {
/* Split chunk. */
link2[-1] = n;
*link = next + n + b;
link = (index_t *)(h->heap + next + n + b);
link[-1] = rem - b;
link[0] = next2;
}
return link2;
} }
next = next2; next = next2;
link = link2; link = link2;