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* bug#48678: [PATCH] lex floats with trailing dot and exponent correctly
@ 2021-05-26 16:56 Mattias Engdegård
  2021-05-26 17:27 ` Eli Zaretskii
  0 siblings, 1 reply; 12+ messages in thread
From: Mattias Engdegård @ 2021-05-26 16:56 UTC (permalink / raw)
  To: 48678

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Motivation: I poured lots of numeric data into Emacs for a computation, but the result weren't as expected at all. Yet my code was correct, and so was the data.

After hours of debugging, it turned out that Emacs reads a number like 1.e6 as the integer 1, not the float 1000000.0. The exponent is silently ignored!

Now Emacs has always treated numbers like 123. as integers rather than floats, but
(1) it's documented,
(2) it's what Common Lisp does, and
(3) it actually doesn't affect the numeric value most of the time.

(Common Lisp probably got this from Maclisp, the rationale being that a trailing dot can be used to write integers in base 10 even when the current input radix is set to something else, something that Emacs Lisp doesn't need.)

Obviously this doesn't apply to 1.e6 which any sane person agrees is the float 1.0e+6 (including Common Lisp).

The attached patch fixes this bug.


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From a0b69a9fc17c42b0c15b28c5894ffb2a1a9327e3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Thu, 20 May 2021 18:26:15 +0200
Subject: [PATCH] Fix lexing of numbers with trailing decimal point and
 exponent

Numbers with a trailing dot and an exponent were incorrectly read as
integers (with the exponent ignored) instead of the floats they should
be.  For example, 1.e6 was read as the integer 1, not 1000000.0 as
every sane person would agree was meant.

Numbers with a trailing dot but no exponent are still read as
integers.

* src/lread.c (string_to_number): Fix float lexing.
* test/src/lread-tests.el (lread-float): Add test.
* doc/lispref/numbers.texi (Float Basics): Clarify syntax.
---
 doc/lispref/numbers.texi |  3 +-
 src/lread.c              | 10 +++---
 test/src/lread-tests.el  | 67 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 74 insertions(+), 6 deletions(-)

diff --git a/doc/lispref/numbers.texi b/doc/lispref/numbers.texi
index 4c5f72126e..d28e15869a 100644
--- a/doc/lispref/numbers.texi
+++ b/doc/lispref/numbers.texi
@@ -237,7 +237,8 @@ Float Basics
 @samp{+15e2}, @samp{15.0e+2}, @samp{+1500000e-3}, and @samp{.15e4} are
 five ways of writing a floating-point number whose value is 1500.
 They are all equivalent.  Like Common Lisp, Emacs Lisp requires at
-least one digit after any decimal point in a floating-point number;
+least one digit after a decimal point in a floating-point number that
+does not have an exponent;
 @samp{1500.} is an integer, not a floating-point number.
 
   Emacs Lisp treats @code{-0.0} as numerically equal to ordinary zero
diff --git a/src/lread.c b/src/lread.c
index bca53a9a37..0b33fd0f25 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -3938,8 +3938,7 @@ string_to_number (char const *string, int base, ptrdiff_t *plen)
   bool signedp = negative | positive;
   cp += signedp;
 
-  enum { INTOVERFLOW = 1, LEAD_INT = 2, DOT_CHAR = 4, TRAIL_INT = 8,
-	 E_EXP = 16 };
+  enum { INTOVERFLOW = 1, LEAD_INT = 2, TRAIL_INT = 4, E_EXP = 16 };
   int state = 0;
   int leading_digit = digit_to_number (*cp, base);
   uintmax_t n = leading_digit;
@@ -3959,7 +3958,6 @@ string_to_number (char const *string, int base, ptrdiff_t *plen)
   char const *after_digits = cp;
   if (*cp == '.')
     {
-      state |= DOT_CHAR;
       cp++;
     }
 
@@ -4008,8 +4006,10 @@ string_to_number (char const *string, int base, ptrdiff_t *plen)
 	    cp = ecp;
 	}
 
-      float_syntax = ((state & (DOT_CHAR|TRAIL_INT)) == (DOT_CHAR|TRAIL_INT)
-		      || (state & ~INTOVERFLOW) == (LEAD_INT|E_EXP));
+      /* A float has digits after the dot or an exponent.
+	 This excludes numbers like "1." which are lexed as integers. */
+      float_syntax = ((state & TRAIL_INT)
+		      || ((state & LEAD_INT) && (state & E_EXP)));
     }
 
   if (plen)
diff --git a/test/src/lread-tests.el b/test/src/lread-tests.el
index f2a60bcf32..dac8f95bc4 100644
--- a/test/src/lread-tests.el
+++ b/test/src/lread-tests.el
@@ -196,4 +196,71 @@ test-inhibit-interaction
     (should-error (read-event "foo: "))
     (should-error (read-char-exclusive "foo: "))))
 
+(ert-deftest lread-float ()
+  (should (equal (read "13") 13))
+  (should (equal (read "+13") 13))
+  (should (equal (read "-13") -13))
+  (should (equal (read "13.") 13))
+  (should (equal (read "+13.") 13))
+  (should (equal (read "-13.") -13))
+  (should (equal (read "13.25") 13.25))
+  (should (equal (read "+13.25") 13.25))
+  (should (equal (read "-13.25") -13.25))
+  (should (equal (read ".25") 0.25))
+  (should (equal (read "+.25") 0.25))
+  (should (equal (read "-.25") -0.25))
+  (should (equal (read "13e4") 130000.0))
+  (should (equal (read "+13e4") 130000.0))
+  (should (equal (read "-13e4") -130000.0))
+  (should (equal (read "13e+4") 130000.0))
+  (should (equal (read "+13e+4") 130000.0))
+  (should (equal (read "-13e+4") -130000.0))
+  (should (equal (read "625e-4") 0.0625))
+  (should (equal (read "+625e-4") 0.0625))
+  (should (equal (read "-625e-4") -0.0625))
+  (should (equal (read "1.25e2") 125.0))
+  (should (equal (read "+1.25e2") 125.0))
+  (should (equal (read "-1.25e2") -125.0))
+  (should (equal (read "1.25e+2") 125.0))
+  (should (equal (read "+1.25e+2") 125.0))
+  (should (equal (read "-1.25e+2") -125.0))
+  (should (equal (read "1.25e-1") 0.125))
+  (should (equal (read "+1.25e-1") 0.125))
+  (should (equal (read "-1.25e-1") -0.125))
+  (should (equal (read "4.e3") 4000.0))
+  (should (equal (read "+4.e3") 4000.0))
+  (should (equal (read "-4.e3") -4000.0))
+  (should (equal (read "4.e+3") 4000.0))
+  (should (equal (read "+4.e+3") 4000.0))
+  (should (equal (read "-4.e+3") -4000.0))
+  (should (equal (read "5.e-1") 0.5))
+  (should (equal (read "+5.e-1") 0.5))
+  (should (equal (read "-5.e-1") -0.5))
+  (should (equal (read "0") 0))
+  (should (equal (read "+0") 0))
+  (should (equal (read "-0") 0))
+  (should (equal (read "0.") 0))
+  (should (equal (read "+0.") 0))
+  (should (equal (read "-0.") 0))
+  (should (equal (read "0.0") 0.0))
+  (should (equal (read "+0.0") 0.0))
+  (should (equal (read "-0.0") -0.0))
+  (should (equal (read "0e5") 0.0))
+  (should (equal (read "+0e5") 0.0))
+  (should (equal (read "-0e5") -0.0))
+  (should (equal (read "0e-5") 0.0))
+  (should (equal (read "+0e-5") 0.0))
+  (should (equal (read "-0e-5") -0.0))
+  (should (equal (read ".0e-5") 0.0))
+  (should (equal (read "+.0e-5") 0.0))
+  (should (equal (read "-.0e-5") -0.0))
+  (should (equal (read "0.0e-5") 0.0))
+  (should (equal (read "+0.0e-5") 0.0))
+  (should (equal (read "-0.0e-5") -0.0))
+  (should (equal (read "0.e-5") 0.0))
+  (should (equal (read "+0.e-5") 0.0))
+  (should (equal (read "-0.e-5") -0.0))
+  )
+
+
 ;;; lread-tests.el ends here
-- 
2.21.1 (Apple Git-122.3)


^ permalink raw reply related	[flat|nested] 12+ messages in thread
end of thread, other threads:[~2021-05-30  4:07 UTC | newest]

Thread overview: 12+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2021-05-26 16:56 bug#48678: [PATCH] lex floats with trailing dot and exponent correctly Mattias Engdegård
2021-05-26 17:27 ` Eli Zaretskii
2021-05-26 22:13   ` Lars Ingebrigtsen
2021-05-27  7:32     ` Andreas Schwab
2021-05-27  7:40       ` Lars Ingebrigtsen
2021-05-27 12:28         ` Mattias Engdegård
2021-05-27 12:36         ` Philipp Stephani
2021-05-27 12:37           ` Philipp Stephani
2021-05-27 12:20   ` Mattias Engdegård
2021-05-29  6:03     ` Lars Ingebrigtsen
2021-05-29  7:47       ` Mattias Engdegård
2021-05-30  4:07         ` Lars Ingebrigtsen

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