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MAINT: Simplify string arena growth strategy #29885

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Merged
seberg merged 1 commit into from
Oct 14, 2025
Merged

MAINT: Simplify string arena growth strategy #29885

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28 changes: 9 additions & 19 deletions numpy/_core/src/multiarray/stringdtype/static_string.c
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Original file line number Diff line number Diff line change
Expand Up @@ -155,8 +155,6 @@ vstring_buffer(npy_string_arena *arena, _npy_static_string_u *string)
return (char *)((size_t)arena->buffer + string->vstring.offset);
}

#define ARENA_EXPAND_FACTOR 1.25

static char *
arena_malloc(npy_string_arena *arena, npy_string_realloc_func r, size_t size)
{
Expand All @@ -168,25 +166,17 @@ arena_malloc(npy_string_arena *arena, npy_string_realloc_func r, size_t size)
else {
string_storage_size = size + sizeof(size_t);
}
if ((arena->size - arena->cursor) <= string_storage_size) {
// realloc the buffer so there is enough room
// first guess is to double the size of the buffer
size_t newsize;
if (arena->size == 0) {
newsize = string_storage_size;
}
else if (((ARENA_EXPAND_FACTOR * arena->size) - arena->cursor) >
string_storage_size) {
newsize = (size_t)(ARENA_EXPAND_FACTOR * arena->size);
if ((arena->size - arena->cursor) < string_storage_size) {
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@seberg seberg Oct 6, 2025

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I changed the <= to < here. == seems fine, i.e. at the end size == cursor which should be valid, no?

size_t minsize = arena->cursor + string_storage_size;
if (minsize < arena->cursor) {
return NULL; // overflow means out of memory
}
else {
newsize = arena->size + string_storage_size;
}
// If there enough room for both the payload and its header
if ((arena->cursor + string_storage_size) > newsize) {
// need extra room beyond the expansion factor, leave some padding
newsize = (size_t)(ARENA_EXPAND_FACTOR * (arena->cursor + string_storage_size));
// Allocate 25% more than needed for this string.
size_t newsize = minsize + minsize / 4;
if (newsize < minsize) {
return NULL; // overflow means out of memory
}

// passing a NULL buffer to realloc is the same as malloc
char *newbuf = r(arena->buffer, newsize);
if (newbuf == NULL) {
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