From 4a56ca5bbfabbb9c581828cd91648346e6b03844 Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Thu, 26 Jul 2018 00:34:10 -0700 Subject: [PATCH] %o and %x can now format signed integers MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Optionally treat integers as signed numbers with %o and %x format specifiers, instead of treating them as a machine-dependent two’s complement representation. This option is more machine-independent, allows formats like "#x%x" to be useful for reading later, and is better-insulated for future changes involving bignums. Setting the new variable ‘binary-as-unsigned’ to nil enables the new behavior (Bug#32252). This is a simplified version of the change proposed in: https://lists.gnu.org/r/emacs-devel/2018-07/msg00763.html I simplified that proposal by omitting bitwidth modifiers, as I could not find an any example uses in the Emacs source code that needed them and doing them correctly would have been quite a bit more work for apparently little benefit. * doc/lispref/strings.texi (Formatting Strings): Document that %x and %o format negative integers in a platform-dependent way. Also, document how to format numbers so that the same values can be read back in. * etc/NEWS: Document the change. * src/editfns.c (styled_format): Treat integers as signed numbers even with %o and %x, if binary-as-unsigned is nil. Support the + and space flags with %o and %x, since they’re about signs. (syms_of_editfns): New variable binary-as-unsigned. * test/src/editfns-tests.el (read-large-integer): Test that maximal integers can be read after printing with all integer formats, if binary-as-unsigned is nil. --- doc/lispref/strings.texi | 17 +++++++++++++++-- etc/NEWS | 9 +++++++++ src/editfns.c | 43 ++++++++++++++++++++++++++++++++++++++----- test/src/editfns-tests.el | 10 ++++++---- 4 files changed, 68 insertions(+), 11 deletions(-) diff --git a/doc/lispref/strings.texi b/doc/lispref/strings.texi index 2fff3c7..3558f17 100644 --- a/doc/lispref/strings.texi +++ b/doc/lispref/strings.texi @@ -922,7 +922,8 @@ Formatting Strings @item %o @cindex integer to octal Replace the specification with the base-eight representation of an -unsigned integer. The object can also be a nonnegative floating-point +integer. Negative integers are formatted in a platform-dependent +way. The object can also be a nonnegative floating-point number that is formatted as an integer, dropping any fraction, if the integer does not exceed machine limits. @@ -935,7 +936,8 @@ Formatting Strings @itemx %X @cindex integer to hexadecimal Replace the specification with the base-sixteen representation of an -unsigned integer. @samp{%x} uses lower case and @samp{%X} uses upper +integer. Negative integers are formatted in a platform-dependent +way. @samp{%x} uses lower case and @samp{%X} uses upper case. The object can also be a nonnegative floating-point number that is formatted as an integer, dropping any fraction, if the integer does not exceed machine limits. @@ -1108,6 +1110,17 @@ Formatting Strings precision is what the local library functions of the @code{printf} family produce. address@hidden formatting numbers for rereading later + If you plan to use @code{read} later on the formatted string to +retrieve a copy of the formatted value, use a specification that lets address@hidden reconstruct the value. To format numbers in this +reversible way you can use @samp{%s} and @samp{%S}, to format just +integers you can also use @samp{%d}, and to format just nonnegative +integers you can also use @samp{#x%x} and @samp{#o%o}. Other formats +may be problematic; for example, @samp{%d} and @samp{%g} can mishandle +NaNs and can lose precision and type, and @samp{#x%x} and @samp{#o%o} +can mishandle negative integers. @xref{Input Functions}. + @node Case Conversion @section Case Conversion in Lisp @cindex upper case diff --git a/etc/NEWS b/etc/NEWS index 995ceb6..089fc40 100644 --- a/etc/NEWS +++ b/etc/NEWS @@ -812,6 +812,15 @@ between two strings. ** 'print-quoted' now defaults to t, so if you want to see (quote x) instead of 'x you will have to bind it to nil where applicable. ++++ +** Numbers formatted via %o or %x may now be formatted as signed integers. +This avoids problems in calls like (read (format "#x%x" -1)), and is +more compatible with bignums, a planned feature. To get this +behavior, set the experimental variable binary-as-unsigned to nil, +and if the new behavior breaks your code please email address@hidden Because %o and %x can now format signed +integers, they now support the + and space flags. + ** To avoid confusion caused by "smart quotes", the reader signals an error when reading Lisp symbols which begin with one of the following quotation characters: ‘’‛“”‟〞＂＇. A symbol beginning with such a diff --git a/src/editfns.c b/src/editfns.c index 1d6040d..df25721 100644 --- a/src/editfns.c +++ b/src/editfns.c @@ -4196,8 +4196,8 @@ contain either numbered or unnumbered %-sequences but not both, except that %% can be mixed with numbered %-sequences. The + flag character inserts a + before any nonnegative number, while a -space inserts a space before any nonnegative number; these flags only -affect %d, %e, %f, and %g sequences, and the + flag takes precedence. +space inserts a space before any nonnegative number; these flags +affect only numeric %-sequences, and the + flag takes precedence. The - and 0 flags affect the width specifier, as described below. The # flag means to use an alternate display form for %o, %x, %X, %e, @@ -4736,10 +4736,22 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message) } else { - /* Don't sign-extend for octal or hex printing. */ uprintmax_t x; + bool negative; if (INTEGERP (arg)) - x = XUINT (arg); + { + if (binary_as_unsigned) + { + x = XUINT (arg); + negative = false; + } + else + { + EMACS_INT i = XINT (arg); + negative = i < 0; + x = negative ? -i : i; + } + } else { double d = XFLOAT_DATA (arg); @@ -4747,8 +4759,13 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message) if (! (0 <= d && d < uprintmax + 1)) xsignal1 (Qoverflow_error, arg); x = d; + negative = false; } - sprintf_bytes = sprintf (sprintf_buf, convspec, prec, x); + sprintf_buf[0] = negative ? '-' : plus_flag ? '+' : ' '; + bool signedp = negative | plus_flag | space_flag; + sprintf_bytes = sprintf (sprintf_buf + signedp, + convspec, prec, x); + sprintf_bytes += signedp; } /* Now the length of the formatted item is known, except it omits @@ -5558,6 +5575,22 @@ functions if all the text being accessed has this property. */); DEFVAR_LISP ("operating-system-release", Voperating_system_release, doc: /* The release of the operating system Emacs is running on. */); + DEFVAR_BOOL ("binary-as-unsigned", + binary_as_unsigned, + doc: /* Non-nil means `format' %x and %o treat integers as unsigned. +This has machine-dependent results. Nil means to treat integers as +signed, which is portable; for example, if N is a negative integer, +(read (format "#x%x") N) returns N only when this variable is nil. + +This variable is experimental; email address@hidden if you need +it to be non-nil. */); + /* For now, default to true if bignums exist, false in traditional Emacs. */ +#ifdef lisp_h_FIXNUMP + binary_as_unsigned = true; +#else + binary_as_unsigned = false; +#endif + defsubr (&Spropertize); defsubr (&Schar_equal); defsubr (&Sgoto_char); diff --git a/test/src/editfns-tests.el b/test/src/editfns-tests.el index c828000..2951270 100644 --- a/test/src/editfns-tests.el +++ b/test/src/editfns-tests.el @@ -165,10 +165,12 @@ transpose-test-get-byte-positions :type 'overflow-error) (should-error (read (substring (format "%d" most-negative-fixnum) 1)) :type 'overflow-error) - (should-error (read (format "#x%x" most-negative-fixnum)) - :type 'overflow-error) - (should-error (read (format "#o%o" most-negative-fixnum)) - :type 'overflow-error) + (let ((binary-as-unsigned nil)) + (dolist (fmt '("%d" "%s" "#o%o" "#x%x")) + (dolist (val (list most-negative-fixnum (1+ most-negative-fixnum) + -1 0 1 + (1- most-positive-fixnum) most-positive-fixnum)) + (should (eq val (read (format fmt val))))))) (should-error (read (format "#32rG%x" most-positive-fixnum)) :type 'overflow-error)) -- 2.7.4