From 198d0338be7c105b6dbd707f98e0c223a8358240 Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Mon, 13 Aug 2012 01:53:10 -0400 Subject: [PATCH] =?UTF-8?q?Add=20a=20primop=20=E2=80=98concatLists?= =?UTF-8?q?=E2=80=99?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This can serve as a generic efficient list builder. For instance, the function ‘catAttrs’ in Nixpkgs can be rewritten from attr: l: fold (s: l: if hasAttr attr s then [(getAttr attr s)] ++ l else l) [] l to attr: l: builtins.concatLists (map (s: if hasAttr attr s then [(getAttr attr s)] else []) l) Statistics before: time elapsed: 1.08683 size of a value: 24 environments allocated: 1384376 (35809568 bytes) list elements: 6946783 (55574264 bytes) list concatenations: 37434 values allocated: 1760440 (42250560 bytes) attribute sets allocated: 392040 right-biased unions: 186334 values copied in right-biased unions: 591137 symbols in symbol table: 18273 number of thunks: 1297673 number of thunks avoided: 1380759 number of attr lookups: 430802 number of primop calls: 628912 number of function calls: 1333544 Statistics after (including new catAttrs): time elapsed: 0.959854 size of a value: 24 environments allocated: 1010198 (26829296 bytes) list elements: 1984878 (15879024 bytes) list concatenations: 30488 values allocated: 1589760 (38154240 bytes) attribute sets allocated: 392040 right-biased unions: 186334 values copied in right-biased unions: 591137 symbols in symbol table: 18274 number of thunks: 1040925 number of thunks avoided: 1038428 number of attr lookups: 438419 number of primop calls: 474844 number of function calls: 959366 --- src/libexpr/eval.cc | 29 +++++++++++++++++++++-------- src/libexpr/eval.hh | 2 ++ src/libexpr/primops.cc | 10 ++++++++++ 3 files changed, 33 insertions(+), 8 deletions(-) diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc index 871dfa64c..5351ca0c3 100644 --- a/src/libexpr/eval.cc +++ b/src/libexpr/eval.cc @@ -912,16 +912,29 @@ void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v) void ExprOpConcatLists::eval(EvalState & state, Env & env, Value & v) { - state.nrListConcats++; Value v1; e1->eval(state, env, v1); - state.forceList(v1); Value v2; e2->eval(state, env, v2); - state.forceList(v2); - state.mkList(v, v1.list.length + v2.list.length); - for (unsigned int n = 0; n < v1.list.length; ++n) - v.list.elems[n] = v1.list.elems[n]; - for (unsigned int n = 0; n < v2.list.length; ++n) - v.list.elems[n + v1.list.length] = v2.list.elems[n]; + Value * lists[2] = { &v1, &v2 }; + state.concatLists(v, 2, lists); +} + + +void EvalState::concatLists(Value & v, unsigned int nrLists, Value * * lists) +{ + nrListConcats++; + + unsigned int len = 0; + for (unsigned int n = 0; n < nrLists; ++n) { + forceList(*lists[n]); + len += lists[n]->list.length; + } + + mkList(v, len); + for (unsigned int n = 0, pos = 0; n < nrLists; ++n) { + unsigned int l = lists[n]->list.length; + memcpy(v.list.elems + pos, lists[n]->list.elems, l * sizeof(Value *)); + pos += l; + } } diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh index 4e66c4dfc..a1f26a056 100644 --- a/src/libexpr/eval.hh +++ b/src/libexpr/eval.hh @@ -232,6 +232,8 @@ public: void mkAttrs(Value & v, unsigned int expected); void mkThunk_(Value & v, Expr * expr); + void concatLists(Value & v, unsigned int nrLists, Value * * lists); + /* Print statistics. */ void printStats(); diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc index aa27df6ad..f5c004044 100644 --- a/src/libexpr/primops.cc +++ b/src/libexpr/primops.cc @@ -931,6 +931,7 @@ static void prim_filter(EvalState & state, Value * * args, Value & v) } +/* Return true if a list contains a given element. */ static void prim_elem(EvalState & state, Value * * args, Value & v) { bool res = false; @@ -944,6 +945,14 @@ static void prim_elem(EvalState & state, Value * * args, Value & v) } +/* Concatenate a list of lists. */ +static void prim_concatLists(EvalState & state, Value * * args, Value & v) +{ + state.forceList(*args[0]); + state.concatLists(v, args[0]->list.length, args[0]->list.elems); +} + + /* Return the length of a list. This is an O(1) time operation. */ static void prim_length(EvalState & state, Value * * args, Value & v) { @@ -1160,6 +1169,7 @@ void EvalState::createBaseEnv() addPrimOp("map", 2, prim_map); addPrimOp("__filter", 2, prim_filter); addPrimOp("__elem", 2, prim_elem); + addPrimOp("__concatLists", 1, prim_concatLists); addPrimOp("__length", 1, prim_length); // Integer arithmetic