Hex numbers are only 32-bits, and probably done so because the 64-bit cannot be used fully due to the way luajit uses double to encode other things, and also that double has only 53-bits mantissa
And this could be probably to avoid (or in more negative sense - force) people to not write code that relies on 64-bit operands if possible, but use 32-bit instead. I think arithmetic with 64-bits might still work, if you deal with uint64_t arrays and do operations in between them, but not with variables
flying around.And although almost all modern architectures have native 64-bit ops (even for 32-bit cpus), almost any algorithms that I've seen out there still rely on 32-bit logical ops.
I could be far off this assumption, but that's my gut feeling. On 5/30/2012 11:18 AM, William Adams wrote:
Yah, I actually use bit.tobit, but, before I did that, the part that actually was biting me was this: avar = 0x100000000ULL This creates a value of cdata type, rather than number. Ignoring this specific usage, should this hex literal be converted to a number or cdata? I'd assume number. This is with beta9, and possibly it's been fixed? -- William =============================== - Shaping clay is easier than digging it out of the ground. http://williamaadams.wordpress.com http://www.thingiverse.com/WilliamAAdams https://github.com/Wiladams ----------------------------------------Date: Wed, 30 May 2012 19:57:04 +0200 From: mike-1205@xxxxxxxxxx To: luajit@xxxxxxxxxxxxx Subject: Re: small gotcha with cdata and number William Adams wrote:As part of a SHA1 calculation, there is this function which will add two 32-bit numbers, and ensure the result is still 32 bits. -- adding 2 32bit numbers, cutting off the remainder on 33rd bit local function w32_add (a,b) return (a+b) % 4294967296 endIck, please don't do that -- it's very slow. Use bit.tobit(a+b) explicitly, if you must. But you can avoid that in most cases, since you're passing these things to other bit.* functions, which implicitly perform the bit.tobit() conversion. In fact, the JIT compiler optimizes a+b passed to a bit operation into a simple 32 bit integer ADD in the machine code. The Lua BitOp distribution has an example MD5 implementation that generates pretty good code with LuaJIT 2.0: http://bitop.luajit.org --Mike
