sizeof have been a compile time constant since inception, however since C99 it can also be used on variable length arrays and for those it of course have to be a runtime operation. Perhaps OpenLDAP used variable length arrays to a huge degree?
strlen() is one clear candidate for some optimizations, often however it is declared as __attribute_pure__ so the compiler should be smart enough to remove redundant calls, but for constant strings a macro like "#define BUFFER_COPY_STRING_CONST(x, y) buffer_copy_string_len(x, y, sizeof(y) - 1)" is useful if curl have many such constant strings passed to various functions that also needs the string length. /HH Den tors 27 jan. 2022 kl 11:52 skrev Timothe Litt via curl-library < curl-library@lists.haxx.se>: > On 27-Jan-22 04:27, Daniel Stenberg via curl-library wrote: > > On Thu, 27 Jan 2022, Gavin Henry wrote: > > I remember in the OpenLDAP project when they removed/reduced the amount of > times sizeofs that were used for performance gains. > > > When is sizeof ever a slow operation? > > As we're only using C89, our sizeof uses are only ever for types/structs, > and I can't see how those are not just converted to a constant at > compile-time by the compiler. > > I'm not familiar with the OpenLDAP exercise, but I also doubt that sizeof > would be slow. Even really, really old, dumb compilers turn them into > constants. > > Perhaps the win was from reducing strlen() calls? They are often > overused, and while they can be optimized to some extent, they are > inherently slow at runtime. Unless a compiler is smart enough to detect a > string constant, where x is a constant replacing strlen(x) with > (sizeof(x)-1) can be a win - which may have been what jogged this memory... > > Timothe Litt > ACM Distinguished Engineer > -------------------------- > This communication may not represent the ACM or my employer's views, > if any, on the matters discussed. > > -- > Unsubscribe: https://lists.haxx.se/listinfo/curl-library > Etiquette: https://curl.haxx.se/mail/etiquette.html >
-- Unsubscribe: https://lists.haxx.se/listinfo/curl-library Etiquette: https://curl.haxx.se/mail/etiquette.html
