#9035: ghci sometimes displays Word32 as Word64 ------------------------------------------------+-------------------------- Reporter: MikeIzbicki | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: GHCi | Version: 7.8.2 Resolution: invalid | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Incorrect result at runtime | (amd64) Test Case: | Difficulty: Blocking: | Unknown | Blocked By: | Related Tickets: ------------------------------------------------+-------------------------- Comment (by carter): you can't do an unsafe coerce between Words and Floats in ghc currently and have it be well defined . Its got nothing to do with boxing, it has to do with Floats and Words actually living is completely distinct groups of registers in the CPU. eg on x86, ghc currently only manipulates words in the general purpose registers, and floats are in SSE registers. (yes, there ARE word manipulation sse instructions, but ghc currently doesn't use them.. yet) NH2 wrote a cute wee lib to cast between float and words https://github.com/nh2/float-cast, which works by writing the input to memory as one type, and reading the memory location back as the other type. I think the only reason some of your code works at all is your unsafe coerce actually will by accident do that "casted memory read" off the heap. The other issue is your Word32 is actually going to be 64bit (1 whoel register) value on 64 bit systems, but Floats are always 32b bits, and your unsafe coerce doesn't actually have any well defined way of mapping between the two. Again, anything resembling that working in current GHC is actually a complete "this is undefined" accident :) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9035#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler