On Thu, Jun 01 2023, Ihor Radchenko <yanta...@posteo.net> wrote:
> Leo Butler <leo.but...@umanitoba.ca> writes:
>
>> In ob-C.el, line 339 has the format specifier
>>
>> (`floatp '("double" "%f"))
>>
>> to print literal floats. However, that format specifier rounds, which
>> can result in errors. I think the correct approach is to print the
>> float without rounding or padding or trying to guess at the desired
>> accuracy (and let the compiler do whatever is needed):
>>
>> (`floatp '("double" "%s"))
>
> Makes sense. Thanks!
>
>> - (`floatp '("double" "%f"))
>> + (`floatp '("double" "%s"))
>
> Please add comment explaining why not %f. Otherwise, it is not fully
> clear why "%s" is used.
Done.
>
>> --- a/testing/examples/ob-C-test.org
>> +++ b/testing/examples/ob-C-test.org
>> @@ -60,6 +60,12 @@
>> return 0;
>> #+end_src
>>
>> +#+source: float_var
>> +#+begin_src cpp :var x=1.123456789012345678 :includes "<iostream>" :results
>> silent
>> +double y = 1.123456789012345678;
>> +std::cout << (x == y);
>> +#+end_src
>
> Please move the source block directly into the test using
> `org-test-with-temp-text'. The test will be more readable then.
>
> `org-test-at-id' should better be used only when necessary in order to
> not jump back and forth when debugging tests.
Ok, I have made the changes requested. Please see the attached patch.
Leo
From 65bddc861c1f439e98d5764f0587e97d4d99a190 Mon Sep 17 00:00:00 2001
From: Leo Butler <leo.but...@umanitoba.ca>
Date: Thu, 1 Jun 2023 13:39:13 -0500
Subject: [PATCH] lisp/ob-C.el: replace %f with %s to prevent unneeded rounding
* lisp/ob-C.el (org-babel-C-val-to-C-type): Floats should be printed
as string literals to prevent rounding introduced by %f format.
* testing/lisp/test-ob-C.el (ob-C/float-var): Test that floats are not
rounded when passed as an org :var.
---
lisp/ob-C.el | 2 +-
testing/lisp/test-ob-C.el | 11 +++++++++++
2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/lisp/ob-C.el b/lisp/ob-C.el
index 3a6e99623..7763c4c07 100644
--- a/lisp/ob-C.el
+++ b/lisp/ob-C.el
@@ -339,7 +339,7 @@ FORMAT can be either a format string or a function which is called with VAL."
(type
(pcase basetype
(`integerp '("int" "%d"))
- (`floatp '("double" "%f"))
+ (`floatp '("double" "%s")) ;; %f rounds, use %s to print the float literally
(`stringp
(list
(if (eq org-babel-c-variant 'd) "string" "const char*")
diff --git a/testing/lisp/test-ob-C.el b/testing/lisp/test-ob-C.el
index b6dbed8e3..8546a48dd 100644
--- a/testing/lisp/test-ob-C.el
+++ b/testing/lisp/test-ob-C.el
@@ -95,6 +95,17 @@
(org-babel-next-src-block 10)
(should (= 42 (org-babel-execute-src-block))))))
+(ert-deftest ob-C/float-var ()
+ "Test that floats are passed without unnecessary rounding."
+ (if (executable-find org-babel-C++-compiler)
+ (org-test-with-temp-text
+"#+source: float_var
+#+begin_src cpp :var x=1.123456789012345678 :includes \"<iostream>\" :results silent
+double y = 1.123456789012345678;
+std::cout << (x == y);
+#+end_src"
+(should (= 1 (org-babel-execute-src-block))))))
+
(ert-deftest ob-C/table ()
"Test of a table output"
(if (executable-find org-babel-C++-compiler)
base-commit: 5b4eebfabdc6a9b4ed223025161a342cb312c1d0
--
2.39.2
