From bedfc8f13c743e29d70a4d4ef9f157f748a8c1cc Mon Sep 17 00:00:00 2001
From: Joe Groff <arcata@gmail.com>
Date: Tue, 20 Oct 2009 22:49:20 -0500
Subject: [PATCH] vif combinator

---
 basis/math/vectors/vectors-docs.factor | 12 +++++++++++-
 basis/math/vectors/vectors.factor      |  9 ++++++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/basis/math/vectors/vectors-docs.factor b/basis/math/vectors/vectors-docs.factor
index 71e86417f5..b831ac7dbe 100644
--- a/basis/math/vectors/vectors-docs.factor
+++ b/basis/math/vectors/vectors-docs.factor
@@ -101,6 +101,7 @@ $nl
     vxor
     vnot
     v?
+    vif
 }
 "Entire vector tests:"
 { $subsections
@@ -534,10 +535,19 @@ HELP: vnot
 { $notes "See " { $link "math-vectors-simd-logic" } " for notes on dealing with vector boolean inputs and results when using SIMD types." } ;
 
 HELP: v?
-{ $values { "mask" "a sequence of booleans" } { "true" "a sequence of numbers" } { "false" "a sequence of numbers" } { "w" "a sequence of numbers" } }
+{ $values { "mask" "a sequence of booleans" } { "true" "a sequence of numbers" } { "false" "a sequence of numbers" } { "result" "a sequence of numbers" } }
 { $description "Creates a new sequence by selecting elements from the " { $snippet "true" } " and " { $snippet "false" } " sequences based on whether the corresponding bits of the " { $snippet "mask" } " sequence are set or not." }
 { $notes "See " { $link "math-vectors-simd-logic" } " for notes on dealing with vector boolean inputs and results when using SIMD types." } ;
 
+HELP: vif
+{ $values { "mask" "a sequence of booleans" } { "true-quot" { $quotation "( -- vector )" } } { "false-quot" { $quotation "( -- vector )" } } { "result" "a sequence" } }
+{ $description "If all of the elements of " { $snippet "mask" } " are true, " { $snippet "true-quot" } " is called and its output value returned. If all of the elements of " { $snippet "mask" } " are false, " { $snippet "false-quot" } " is called and its output value returned. Otherwise, both quotations are called and " { $snippet "mask" } " is used to select elements from each output as with " { $link v? } "." }
+{ $notes "See " { $link "math-vectors-simd-logic" } " for notes on dealing with vector boolean inputs and results when using SIMD types."
+$nl
+"For most conditional SIMD code, unless a case is exceptionally expensive to compute, it is usually most efficient to just compute all cases and blend them with " { $link v? } " instead of using " { $snippet "vif" } "." } ;
+
+{ v? vif } related-words
+
 HELP: vany?
 { $values { "v" "a sequence of booleans" } { "?" "a boolean" } }
 { $description "Returns true if any element of " { $snippet "v" } " is true." }
diff --git a/basis/math/vectors/vectors.factor b/basis/math/vectors/vectors.factor
index 49ee6c3873..81af5c12d2 100644
--- a/basis/math/vectors/vectors.factor
+++ b/basis/math/vectors/vectors.factor
@@ -142,9 +142,16 @@ M: simd-128 vshuffle ( u perm -- v )
 : vunordered? ( u v -- w ) [ unordered? ] 2map ;
 : v=  ( u v -- w ) [ =   ] 2map ;
 
-: v? ( mask true false -- w )
+: v? ( mask true false -- result )
     [ vand ] [ vandn ] bi-curry* bi vor ; inline
 
+:: vif ( mask true-quot false-quot -- result )
+    {
+        { [ mask vall?  ] [ true-quot  call ] }
+        { [ mask vnone? ] [ false-quot call ] }
+        [ mask true-quot call false-quot call v? ]
+    } cond ; inline
+
 : vfloor    ( u -- v ) [ floor ] map ;
 : vceiling  ( u -- v ) [ ceiling ] map ;
 : vtruncate ( u -- v ) [ truncate ] map ;