From: Taylor R Campbell <campbell@mumble.net>
Date: Fri, 30 Nov 2018 06:48:05 +0000 (+0000)
Subject: Define and expose flo:precision.
X-Git-Tag: mit-scheme-pucked-10.1.7~3^2~95
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=4110934060a92803966e70b39c2ee6e25bb25d08;p=mit-scheme.git

Define and expose flo:precision.

This is the same as flo:significand-digits-base-2, but its name
doesn't imply base 2 -- it refers to whatever the floating-point
radix is.  Not that we're likely to do decimal floating-point ever,
but maybe you might want to write code that could be used in another
environment that does.
---

diff --git a/src/relnotes/flonum b/src/relnotes/flonum
index cd953f323..e42ef8fb6 100644
--- a/src/relnotes/flonum
+++ b/src/relnotes/flonum
@@ -4,7 +4,10 @@ New flonum-related definitions:
   always 2 but useful for assertions if you want to future-proof code
   that assumes it with a noisy failure in case we ever violate the
   assumption.
-- flo:radix. - Floating-point radix as a flonum.
+. flo:radix. - Floating-point radix as a flonum.
+. flo:precision - Number of digits in a significand, including the hidden
+  one bit for normal binary floating-point numbers.  For binary64
+  floating-point, this is 53.
 . flo:error-bound - Greatest possible relative error in rounding to nearest.
 . flo:log-error-bound = (log flo:error-bound)
 . flo:ulp-of-one - Distance from 1 to next greater floating-point number.
diff --git a/src/runtime/arith.scm b/src/runtime/arith.scm
index 87e25a1cd..ae273999f 100644
--- a/src/runtime/arith.scm
+++ b/src/runtime/arith.scm
@@ -95,6 +95,7 @@ USA.
 
 (define-integrable flo:radix 2)
 (define-integrable flo:radix. 2.)
+(define flo:precision)
 (define flo:ulp-of-one)
 (define flo:error-bound)
 (define flo:log-error-bound)
@@ -119,6 +120,7 @@ USA.
 
 (define (initialize-microcode-dependencies!)
   (let ((p microcode-id/floating-mantissa-bits))
+    (set! flo:precision p)
     (set! flo:significand-digits-base-2 p)
     ;; Add two here because first and last digits may be
     ;; "partial" in the sense that each represents less than the
diff --git a/src/runtime/runtime.pkg b/src/runtime/runtime.pkg
index 5777e63ef..71c552823 100644
--- a/src/runtime/runtime.pkg
+++ b/src/runtime/runtime.pkg
@@ -3403,6 +3403,7 @@ USA.
 	  flo:log-error-bound
 	  flo:normal-exponent-max
 	  flo:normal-exponent-min
+	  flo:precision
 	  flo:radix
 	  flo:radix.
 	  flo:significand-digits-base-10
diff --git a/tests/runtime/test-arith.scm b/tests/runtime/test-arith.scm
index acfee8048..0de60324a 100644
--- a/tests/runtime/test-arith.scm
+++ b/tests/runtime/test-arith.scm
@@ -943,7 +943,6 @@ USA.
                           (- z))))))
 
 (assert (= flo:radix 2))
-(define flo:precision flo:significand-digits-base-2)
 
 (define-enumerated-test 'exact->inexact
   `((,(+ 1 (expt flo:radix flo:precision))