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:

https://github.com/NixOS/nixpkgs/pull/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: #2339
This commit is contained in:
aszlig 2018-08-29 00:23:51 +02:00
parent c651b7bdc9
commit 0ad643ed5c
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GPG key ID: 684089CE67EBB691
2 changed files with 7 additions and 3 deletions

View file

@ -12,6 +12,8 @@
%{
#include <boost/lexical_cast.hpp>
#include "nixexpr.hh"
#include "parser-tab.hh"
@ -124,9 +126,11 @@ or { return OR_KW; }
{ID} { yylval->id = strdup(yytext); return ID; }
{INT} { errno = 0;
yylval->n = strtol(yytext, 0, 10);
if (errno != 0)
try {
yylval->n = boost::lexical_cast<int64_t>(yytext);
} catch (const boost::bad_lexical_cast &) {
throw ParseError(format("invalid integer '%1%'") % yytext);
}
return INT;
}
{FLOAT} { errno = 0;

View file

@ -43,7 +43,7 @@ class XMLWriter;
class JSONPlaceholder;
typedef long NixInt;
typedef int64_t NixInt;
typedef double NixFloat;
/* External values must descend from ExternalValueBase, so that