Commits on Aug 28, 2018

1. libexpr: Use int64_t for NixInt …

   Using a 64bit integer on 32bit systems will come with a bit of a
   performance overhead, but given that Nix doesn't use a lot of integers
   compared to other types, I think the overhead is negligible also
   considering that 32bit systems are in decline.
   
   The biggest advantage however is that when we use a consistent integer
   size across all platforms it's less likely that we miss things that we
   break due to that. One example would be:
   
   NixOS/nixpkgs#44233
   
   On Hydra it will evaluate, because the evaluator runs on a 64bit
   machine, but when evaluating the same on a 32bit machine it will fail,
   so using 64bit integers should make that consistent.
   
   While the change of the type in value.hh is rather easy to do, we have a
   few more options available for doing the conversion in the lexer:
   
     * Via an #ifdef on the architecture and using strtol() or strtoll()
       accordingly depending on which architecture we are. For the #ifdef
       we would need another AX_COMPILE_CHECK_SIZEOF in configure.ac.
     * Using istringstream, which would involve copying the value.
     * As we're already using boost, lexical_cast might be a good idea.
   
   Spoiler: I went for the latter, first of all because lexical_cast does
   have an overload for const char* and second of all, because it doesn't
   involve copying around the input string. Also, because istringstream
   seems to come with a bigger overhead than boost::lexical_cast:
   
   https://www.boost.org/doc/libs/release/doc/html/boost_lexical_cast/performance.html
   
   The first method (still using strtol/strtoll) also wasn't something I
   pursued further, because it is also locale-aware which I doubt is what
   we want, given that the regex for int is [0-9]+.
   
   Signed-off-by: aszlig <aszlig@nix.build>
   Fixes: NixOS#2339

   

   aszlig committed Aug 28, 2018
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