Log2 is pretty fast. We use BSR if available.
https://c9x.me/x86/html/file_module_x86_id_20.html > On Jun 5, 2020, at 3:01 PM, Doug Coleman <doug.cole...@gmail.com> wrote: > > > As long as you can fully round-trip the integer, it doesn't matter how many > bytes you use. > > nano-count dup 4 >be be> = . > f > > nano-count dup 8 >be be> = . > t > > nano-count dup 128 >be be> = . > t > > > ``log2 1 +`` will give you the required number of bits to store an integer. > You will want to round up to a power of 8 bits or a power of two bytes. > > USE: math.bitwise > nano-count dup dup log2 1 + bits = > >> On Fri, Jun 5, 2020 at 4:44 PM Alexander Ilin <ajs...@yandex.ru> wrote: >> Hello again! >> >> My specific example is the following. I want to put the output of >> `nano-count` into a `byte-array`, which is fed into a hash. The current >> value of `nano-count` is one of the sources of randomness gathered from the >> system and poured into the hash. To convert the integer value into a >> `byte-array` there are `>le` and `>be`, but they require the number of bytes >> as a parameter. The question is, what should I supply for the value received >> from `nano-count`? >> >> And the bigger question is, given an integer value, is there a way to >> interrogate it about its byte size, i.e. the minimum number of bytes it >> takes to hold the value without truncation and without leading zeroes: >> >> Value -- MinSize >> 0 -- 1 >> 255 -- 1 >> 256 -- 2 >> 65535 -- 2 >> 65536 -- 3 >> etc. >> >> I would expect such information to be available somewhere without doing the >> power of two calculations in a loop. >> >> 23.03.2020, 05:41, "Doug Coleman" <doug.cole...@gmail.com>: >> For Factor, integers are either fixnum or bignum size. For C, you tell it >> how many bytes it occupies according to the C header. Generally the sizes >> are the same across platforms. If they aren't, you might need two different >> STRUCT: declarations like in basis/unix/stat/linux/32/32.factor and >> basis/unix/stat/linux/64/64.factor. >> >> The main point -- function signatures and struct declarations usually handle >> the integer sizes and you shouldn't have to think much about it. Do you have >> a specific example? >> >> >> >> Earlier I wrote: >> One more question. I want to convert an integer into a byte-array >> containing its bytes. In my use case it was the return value of the >> nano-count, but the question is general: how can I get the bytes of an >> integer. >> >> For floats there are primitives like float>bits and double>bits, and for >> integers there is >le and >be, but for the latter two I need to specify the >> size in bytes. Is there a way to ask an integer how many bytes it occupies? >> Because from the documentation it's not clear at all how many bytes >> nano-count would return, and it may vary depending on the current platform. >> What am I missing? >> _______________________________________________ >> Factor-talk mailing list >> Factor-talk@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/factor-talk > _______________________________________________ > Factor-talk mailing list > Factor-talk@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/factor-talk
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