From: Taylor R Campbell <campbell@mumble.net>
Date: Thu, 29 Nov 2018 02:09:57 +0000 (+0000)
Subject: Update some release notes on floating-point stuff.
X-Git-Tag: mit-scheme-pucked-10.1.7~3^2~131
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=0884cbcecf90540748e900eddb221d5448b4dc7b;p=mit-scheme.git

Update some release notes on floating-point stuff.
---

diff --git a/src/relnotes/bug-compare-nan b/src/relnotes/bug-compare-nan
index aabd0ee9a..90bc97a3b 100644
--- a/src/relnotes/bug-compare-nan
+++ b/src/relnotes/bug-compare-nan
@@ -1,2 +1,10 @@
 Bug fix: The <= and >= procedures now return false for NaN inputs; they
-previously returned true.
+previously returned true.  Additionally, on amd64, all of the numerical
+comparison routines now raise floating-point exceptions for NaN inputs
+according to the rules of IEEE 754-2008, which can be tested and can
+trap.  (The new procedures flo:safe<, flo:safe<= flo:safe>, flo:safe>=,
+flo:safe=, flo:safe<>, and flo:unordered? avoid exceptions.)
+
+(The i386 compiler back end does not correctly raise floating-point
+exceptions, and the C and SVM back ends may or may not depending on
+your C compiler's IEEE 754-2008 conformance.)
diff --git a/src/relnotes/flonum b/src/relnotes/flonum
index b1a7c05d9..b74dc3afc 100644
--- a/src/relnotes/flonum
+++ b/src/relnotes/flonum
@@ -58,3 +58,30 @@ New flonum-related definitions:
   - nan
 . (flo:subnormal? x) is true if x is subnormal; false if zero, normal,
   infinite, or NaN
+- (flo:safe-zero? x) is true if x is zero; false if subnormal, normal,
+  infinite, or NaN.  flo:zero? may raise an exception; flo:safe-zero?
+  never does.
+- (flo:safe-negative? x) returns true if x has negative sign, false if
+  x has positive sign.  Note that (flo:negative? 0.) and (flo:negative?
+  -0.) both return false, while (flo:safe-negative? -0.) returns true.
+  Also, flo:negative? may raise a invalid-operation exception if an
+  input is NaN, while flo:safe-negative?  does not.
+- (flo:safe< x y), (flo:safe<= x y), (flo:safe> x y), (flo:safe>= x y),
+  (flo:safe= x y), (flo:safe<> x y), (flo:unordered? x y) perform
+  unordered floating-point comparisons and never raise exceptions.
+- (flo:compare x y) and (flo:safe-compare x y) return a four-way
+  comparison of two floating-point numbers: negative if x < y, zero if
+  x = y, positive if x > y, and #f if one or both arguments is NaN.
+  flo:compare may raise an invalid-operation exception;
+  flo:safe-compare never does.
+- (flo:<> x y) returns true if x is less or greater than y, false if
+  equal or unordered.  May raise an invalid-operation exception.
+- (flo:min-mag x y) and (flo:max-mag x y) return the number of lesser
+  or greater magnitude, as in minNumMag and maxNumMag of IEEE 754-2008.
+- (flo:make-nan negative? quiet? payload) returns a NaN with the
+  specified payload, which must not exceed (- (expt 2
+  flo:significand-digits-base-2 2) 1).
+- (flo:nan-quiet? nan) returns true for quiet NaNs, false for
+  signalling NaNs.
+- (flo:nan-payload nan) returns the payload of NaN, an integer between
+  0 (inclusive) and 2^51 (exclusive).