From e11d9c846e77aff52867c3c18133b7d321e09a29 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Fri, 21 Jun 2019 12:20:06 -0600
Subject: [PATCH] fix flround on [-0.5, 0.0)

original commit: 9679b21d99477a077b226bc279a6d68ebbd7ce5b
---
 mats/5_3.ms  | 2 ++
 mats/fl.ms   | 5 +++++
 s/library.ss | 8 +++++---
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/mats/5_3.ms b/mats/5_3.ms
index d8205f1b71..ca8d4b7a37 100644
--- a/mats/5_3.ms
+++ b/mats/5_3.ms
@@ -2186,6 +2186,8 @@
     (fl= (round 0.5000000000000001) 1.0)
     (eqv? (round 0.0) 0.0)
     (eqv? (round -0.0) -0.0)
+    (eqv? (round -0.5) -0.0)
+    (eqv? (round -0.6) -1.0)
  )
 
 (mat abs
diff --git a/mats/fl.ms b/mats/fl.ms
index d953c8f6ed..4e38a1b14b 100644
--- a/mats/fl.ms
+++ b/mats/fl.ms
@@ -654,6 +654,11 @@
     (fl= (flround 2.5) 2.0)
     (fl= (flround 0.5000000000000000) 0.0)
     (fl= (flround 0.5000000000000001) 1.0)
+    (eqv? (flround 0.0) 0.0)
+    (eqv? (flround -0.0) -0.0)
+    (eqv? (flround 0.5) 0.0)
+    (eqv? (flround -0.5) -0.0)
+    (fl= (flround -0.5000000000000001) -1.0)
  )
 
 (mat flinteger?
diff --git a/s/library.ss b/s/library.ss
index f9698506cf..f9dd164955 100644
--- a/s/library.ss
+++ b/s/library.ss
@@ -630,9 +630,11 @@
           (if (fl< x threshold+)
               (fl- (fl+ x threshold+) threshold+)
               x)
-          (if (fl> x threshold-)
-              (fl- (fl+ x threshold-) threshold-)
-              x))))
+          (if (fl>= x -0.5)
+              -0.0 ; keep negative
+              (if (fl> x threshold-)
+                  (fl- (fl+ x threshold-) threshold-)
+                  x)))))
 
 ;;; The generic comparison entries assume the fixnum case is inlined.