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Add builtin function "partition"

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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).
This commit is contained in:
Eelco Dolstra 2016-08-29 17:28:20 +02:00
parent c0a7b84748
commit 26d92017d3
7 changed files with 54 additions and 10 deletions
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35
src/libexpr/primops.cc
View file

@ -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);