Re: [PATCH] build: Fix potential type error when generating human-friendly byte count strings.

[Steve Sprang <steve.sprang@gmail.com>]

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Sure thing. Here you go.

-Steve

On Wed, Sep 9, 2015 at 7:42 PM, Mark H Weaver <mhw@netris.org> wrote:

> Steve Sprang <steve.sprang@gmail.com> writes:
>
> > This is a follow up tweak to my previous "progress bar" patch. With a
> > really slow throughput it's possible to get fractional sub-KiB byte
> > counts, so I added some additional number massaging.
>
> Sounds good!  Looks good to me except for a few minor nits on this
> auxiliary procedure:
>
> > +(define (number->integer n)
> > +  "Given an arbitrary number N, round it and return the exact result."
> > +  (inexact->exact (round n)))
>
> How about calling it "nearest-exact-integer"?  Also, it makes sense only
> for real numbers, not arbitrary numbers, and the variable name N is
> conventionally used to denote natural numbers, and X for real numbers.
>
> So, how about naming the argument 'x', and using something closer to the
> following docstring:
>
>   "Given a real number X, return the nearest exact integer, with ties
> going to the nearest exact even integer."
>
> Otherwise, looks good to me.  Can you send an updated patch?
>
>       Mark
>

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From 922d9ae8b6f2c13638b49fcc8b79f8d464f01244 Mon Sep 17 00:00:00 2001
From: Steve Sprang <scs@stevesprang.com>
Date: Wed, 9 Sep 2015 13:59:52 -0700
Subject: [PATCH] build: Fix potential type error when generating
 human-friendly byte count strings.

* guix/build/download.scm (nearest-exact-integer): New function.
  (seconds->string): Use new rounding function.
  (byte-count->string):  Use new rounding function.
---
 guix/build/download.scm | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/guix/build/download.scm b/guix/build/download.scm
index 6e85174..31d60fb 100644
--- a/guix/build/download.scm
+++ b/guix/build/download.scm
@@ -49,6 +49,11 @@
   ;; Size of the HTTP receive buffer.
   65536)
 
+(define (nearest-exact-integer x)
+  "Given a real number X, return the nearest exact integer, with ties going to
+the nearest exact even integer."
+  (inexact->exact (round x)))
+
 (define (duration->seconds duration)
   "Return the number of seconds represented by DURATION, a 'time-duration'
 object, as an inexact number."
@@ -60,7 +65,7 @@ object, as an inexact number."
 format."
   (if (not (number? duration))
       "00:00:00"
-      (let* ((total-seconds (inexact->exact (round duration)))
+      (let* ((total-seconds (nearest-exact-integer duration))
              (extra-seconds (modulo total-seconds 3600))
              (hours         (quotient total-seconds 3600))
              (mins          (quotient extra-seconds 60))
@@ -75,8 +80,8 @@ way."
         (GiB (expt 1024. 3))
         (TiB (expt 1024. 4)))
     (cond
-     ((< size KiB) (format #f "~dB" (inexact->exact size)))
-     ((< size MiB) (format #f "~dKiB" (inexact->exact (round (/ size KiB)))))
+     ((< size KiB) (format #f "~dB"     (nearest-exact-integer size)))
+     ((< size MiB) (format #f "~dKiB"   (nearest-exact-integer (/ size KiB))))
      ((< size GiB) (format #f "~,1fMiB" (/ size MiB)))
      ((< size TiB) (format #f "~,2fGiB" (/ size GiB)))
      (else         (format #f "~,3fTiB" (/ size TiB))))))
-- 
2.5.0