Re: [Libguestfs] [PATCH nbdkit 1/2] common/utils/vector: Add comments to generic_vector_reserve

This commit makes no changes, it simply adds comments and breaks out the multiplcation into a local variable. --- common/utils/vector.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-) diff --git a/common/utils/vector.c b/common/utils/vector.c index d7120399..dff051e9 100644 --- a/common/utils/vector.c +++ b/common/utils/vector.c @@ -42,20 +42,31 @@ int generic_vector_reserve (struct generic_vector *v, size_t n, size_t itemsize) { void *newptr; - size_t reqcap, newcap; + size_t reqcap, reqbytes, newcap, newbytes; + /* New capacity requested. We must allocate this minimum (or fail). */ reqcap = v->cap + n; - if (reqcap * itemsize < v->cap * itemsize) { + reqbytes = reqcap * itemsize; + if (reqbytes < v->cap * itemsize) { errno = ENOMEM; return -1; /* overflow */ } + /* However for the sake of optimization, scale buffer by 3/2 so that + * repeated reservations don't call realloc often. + */ newcap = v->cap + (v->cap + 1) / 2; + newbytes = newcap * itemsize; - if (newcap * itemsize < reqcap * itemsize) + if (newbytes < reqbytes) { + /* If that either overflows or is less than the minimum requested, + * fall back to the requested capacity. + */ newcap = reqcap; + newbytes = reqbytes; + } - newptr = realloc (v->ptr, newcap * itemsize); + newptr = realloc (v->ptr, newbytes); if (newptr == NULL) return -1; v->ptr = newptr;