File 2965-Optimize-mwc59-float-generation-for-speed.... of Package erlang

Overview Repositories Revisions Requests Users Attributes Meta

File 2965-Optimize-mwc59-float-generation-for-speed.patch of Package erlang (Revision f663696ed814cd9e073edce69f588c34)

Currently displaying revision f663696ed814cd9e073edce69f588c34 , Show latest

From 0ca7af2271414e8610e02148f604dcdae1fde9a9 Mon Sep 17 00:00:00 2001
From: Raimo Niskanen <raimo@erlang.org>
Date: Tue, 10 May 2022 16:55:24 +0200
Subject: [PATCH 5/8] Optimize mwc59 float generation for speed

High bits are better, but the low 53 bits contain fairly many
hight bits, and the code for generating a float becomes faster,
so sacrifice a little quality for a little speed.
---
 lib/stdlib/src/rand.erl        | 8 ++++----
 lib/stdlib/test/rand_SUITE.erl | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/lib/stdlib/src/rand.erl b/lib/stdlib/src/rand.erl
index ac61acd955..5f8d3a4c59 100644
--- a/lib/stdlib/src/rand.erl
+++ b/lib/stdlib/src/rand.erl
@@ -1533,10 +1533,10 @@ mwc59_value(CX1) -> % when is_integer(CX1), 1 =< CX1, CX1 < ?MWC59_P ->
 
 -spec mwc59_float(CX :: mwc59_state()) -> V :: float().
 mwc59_float(CX1) ->
-    CX = ?MASK(59, CX1),
-    CX2 = CX bxor ?BSL(59, CX, ?MWC59_XS1),
-    CX3 = CX2 bxor ?BSL(59, CX2, ?MWC59_XS2),
-    (CX3 bsr (59-53)) * ?TWO_POW_MINUS53.
+    CX = ?MASK(53, CX1),
+    CX2 = CX bxor ?BSL(53, CX, ?MWC59_XS1),
+    CX3 = CX2 bxor ?BSL(53, CX2, ?MWC59_XS2),
+    CX3 * ?TWO_POW_MINUS53.
 
 -spec mwc59_seed() -> CX :: mwc59_state().
 mwc59_seed() ->
diff --git a/lib/stdlib/test/rand_SUITE.erl b/lib/stdlib/test/rand_SUITE.erl
index 5f3df66bee..f1b2a33808 100644
--- a/lib/stdlib/test/rand_SUITE.erl
+++ b/lib/stdlib/test/rand_SUITE.erl
@@ -237,7 +237,7 @@ mwc59_api(CX0, 0) ->
     W = 269866568368142303,
     {W, W} = {W0, W},
     F0 = rand:mwc59_float(CX0),
-    F = (W bsr (59-53)) * (1 / (1 bsl 53)),
+    F = (W band ((1 bsl 53)-1)) * (1 / (1 bsl 53)),
     {F, F} = {F0, F},
     ok;
 mwc59_api(CX, N)
-- 
2.35.3

Places

File 2965-Optimize-mwc59-float-generation-for-speed.patch of Package erlang (Revision f663696ed814cd9e073edce69f588c34)

Places