From b9e5b908ed29bfb6cd82837f9f57293c1f63e999 Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Mon, 13 Aug 2012 01:05:35 -0400 Subject: [PATCH] =?UTF-8?q?Provide=20an=20efficient=20implementation=20of?= =?UTF-8?q?=20=E2=80=98elem=E2=80=99?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The one in Nixpkgs is O(n^2), this one is O(n). Big reduction in the number of list allocations. Statistics before (on a NixOS system config): time elapsed: 1.17982 size of a value: 24 environments allocated: 1543334 (39624560 bytes) list elements: 9612638 (76901104 bytes) list concatenations: 37434 values allocated: 1854933 (44518392 bytes) attribute sets allocated: 392040 right-biased unions: 186334 values copied in right-biased unions: 591137 symbols in symbol table: 18272 number of thunks: 1392467 number of thunks avoided: 1507311 number of attr lookups: 430801 number of primop calls: 691600 number of function calls: 1492502 Statistics after: 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 --- src/libexpr/primops.cc | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc index db7aa9e89..aa27df6ad 100644 --- a/src/libexpr/primops.cc +++ b/src/libexpr/primops.cc @@ -880,7 +880,8 @@ static void prim_head(EvalState & state, Value * * args, Value & v) /* Return a list consisting of everything but the the first element of - a list. */ + a list. Warning: this function takes O(n) time, so you probably + don't want to use it! */ static void prim_tail(EvalState & state, Value * * args, Value & v) { state.forceList(*args[0]); @@ -930,6 +931,19 @@ static void prim_filter(EvalState & state, Value * * args, Value & v) } +static void prim_elem(EvalState & state, Value * * args, Value & v) +{ + bool res = false; + state.forceList(*args[1]); + for (unsigned int n = 0; n < args[1]->list.length; ++n) + if (state.eqValues(*args[0], *args[1]->list.elems[n])) { + res = true; + break; + } + mkBool(v, res); +} + + /* Return the length of a list. This is an O(1) time operation. */ static void prim_length(EvalState & state, Value * * args, Value & v) { @@ -1145,8 +1159,9 @@ void EvalState::createBaseEnv() addPrimOp("__tail", 1, prim_tail); addPrimOp("map", 2, prim_map); addPrimOp("__filter", 2, prim_filter); + addPrimOp("__elem", 2, prim_elem); addPrimOp("__length", 1, prim_length); - + // Integer arithmetic addPrimOp("__add", 2, prim_add); addPrimOp("__sub", 2, prim_sub);