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Add builtin function "partition"

The implementation of "partition" in Nixpkgs is O(n^2) (because of the
use of ++), and for some reason was causing stack overflows in
multi-threaded evaluation (not sure why).

This reduces "nix-env -qa --drv-path" runtime by 0.197s and memory
usage by 298 MiB (in non-Boehm mode).
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edolstra committed Aug 29, 2016
1 parent c0a7b84 commit 26d92017d3b36cff940dcb7d1611c42232edb81a
@@ -293,6 +293,8 @@ EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
, sColumn(symbols.create("column"))
, sFunctor(symbols.create("__functor"))
, sToString(symbols.create("__toString"))
, sRight(symbols.create("right"))
, sWrong(symbols.create("wrong"))
, store(store)
, baseEnv(allocEnv(128))
, staticBaseEnv(false, 0)
@@ -71,7 +71,8 @@ public:

const Symbol sWith, sOutPath, sDrvPath, sType, sMeta, sName, sValue,
sSystem, sOverrides, sOutputs, sOutputName, sIgnoreNulls,
sFile, sLine, sColumn, sFunctor, sToString;
sFile, sLine, sColumn, sFunctor, sToString,
sRight, sWrong;
Symbol sDerivationNix;

/* If set, force copying files to the Nix store even if they
@@ -12,15 +12,6 @@ static void skipWhitespace(const char * & s)
}


#if HAVE_BOEHMGC
typedef std::vector<Value *, gc_allocator<Value *> > ValueVector;
typedef std::map<Symbol, Value *, std::less<Symbol>, gc_allocator<Value *> > ValueMap;
#else
typedef std::vector<Value *> ValueVector;
typedef std::map<Symbol, Value *> ValueMap;
#endif


static string parseJSONString(const char * & s)
{
string res;
@@ -1443,6 +1443,40 @@ static void prim_sort(EvalState & state, const Pos & pos, Value * * args, Value
}


static void prim_partition(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
state.forceFunction(*args[0], pos);
state.forceList(*args[1], pos);

auto len = args[1]->listSize();

ValueVector right, wrong;

for (unsigned int n = 0; n < len; ++n) {
auto vElem = args[1]->listElems()[n];
state.forceValue(*vElem);
Value res;
state.callFunction(*args[0], *vElem, res, pos);
if (state.forceBool(res))
right.push_back(vElem);
else
wrong.push_back(vElem);
}

state.mkAttrs(v, 2);

Value * vRight = state.allocAttr(v, state.sRight);
state.mkList(*vRight, right.size());
memcpy(vRight->listElems(), right.data(), sizeof(Value *) * right.size());

Value * vWrong = state.allocAttr(v, state.sWrong);
state.mkList(*vWrong, wrong.size());
memcpy(vWrong->listElems(), wrong.data(), sizeof(Value *) * wrong.size());

v.attrs->sort();
}


/*************************************************************
* Integer arithmetic
*************************************************************/
@@ -1881,6 +1915,7 @@ void EvalState::createBaseEnv()
addPrimOp("__all", 2, prim_all);
addPrimOp("__genList", 2, prim_genList);
addPrimOp("__sort", 2, prim_sort);
addPrimOp("__partition", 2, prim_partition);

// Integer arithmetic
addPrimOp("__add", 2, prim_add);
@@ -250,4 +250,13 @@ void mkPath(Value & v, const char * s);
size_t valueSize(Value & v);


#if HAVE_BOEHMGC
typedef std::vector<Value *, gc_allocator<Value *> > ValueVector;
typedef std::map<Symbol, Value *, std::less<Symbol>, gc_allocator<Value *> > ValueMap;
#else
typedef std::vector<Value *> ValueVector;
typedef std::map<Symbol, Value *> ValueMap;
#endif


}
@@ -0,0 +1 @@
{ right = [ 0 2 4 6 8 10 100 102 104 106 108 110 ]; wrong = [ 1 3 5 7 9 101 103 105 107 109 ]; }
@@ -0,0 +1,5 @@
with import ./lib.nix;

builtins.partition
(x: x / 2 * 2 == x)
(builtins.concatLists [ (range 0 10) (range 100 110) ])

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