* Re: Byte swapping and bindat
[not found] ` <83mtekzf9f.fsf@gnu.org>
@ 2022-06-10 21:42 ` Stefan Monnier
2022-06-11 0:55 ` Po Lu
2022-06-11 5:45 ` Eli Zaretskii
0 siblings, 2 replies; 3+ messages in thread
From: Stefan Monnier @ 2022-06-10 21:42 UTC (permalink / raw)
To: Eli Zaretskii; +Cc: EMACS development team
Eli Zaretskii [2022-06-10 18:53:32] wrote:
>> Date: Fri, 10 Jun 2022 09:32:31 -0400
>> From: Stefan Monnier via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>
>>
>> (let* ((threshold 32)
>> (type (bindat-type (kind uint 8)
>> (length sint 32 (> kind threshold)))))
>> (list (bindat-unpack type "\x10\x00\x00\x01\x01")
>> (bindat-unpack type "\x80\x00\x00\x01\x01")))
>> =>
>> (((kind . 16) (length . 257))
>> ((kind . 128) (length . 16842752)))
>
> It would be nice to have sint documented in the ELisp manual...
Good point. I think it would also be nice to unify `uint` and `uintr`.
What about the patch below?
Stefan
diff --git a/doc/lispref/processes.texi b/doc/lispref/processes.texi
index 55fb93ec5a8..63570d2117f 100644
--- a/doc/lispref/processes.texi
+++ b/doc/lispref/processes.texi
@@ -3470,13 +3470,15 @@ Bindat Types
@itemx byte
Unsigned byte, with length 1.
-@item uint @var{bitlen}
-Unsigned integer in network byte order, with @var{bitlen} bits.
+@item uint @var{bitlen} &optional @var{le}
+Unsigned integer in network byte order (big-endian), with @var{bitlen} bits.
@var{bitlen} has to be a multiple of 8.
+If @var{le} is non-@code{nil}, then use little-endian.
-@item uintr @var{bitlen}
-Unsigned integer in little endian order, with @var{bitlen} bits.
+@item sint @var{bitlen} @var{le}
+Signed integer in network byte order (big-endian), with @var{bitlen} bits.
@var{bitlen} has to be a multiple of 8.
+If @var{le} is non-@code{nil}, then use little-endian.
@item str @var{len}
Unibyte string (@pxref{Text Representations}) of length @var{len} bytes.
diff --git a/lisp/emacs-lisp/bindat.el b/lisp/emacs-lisp/bindat.el
index 5f3c772983a..48ae7c8545b 100644
--- a/lisp/emacs-lisp/bindat.el
+++ b/lisp/emacs-lisp/bindat.el
@@ -77,7 +77,7 @@
;; (bindat-type
;; (type u8)
;; (opcode u8)
-;; (length uintr 32) ;; little endian order
+;; (length uint 32 t) ;; little endian order
;; (id strz 8)
;; (data vec length)
;; (_ align 4)))
@@ -663,14 +663,17 @@ bindat--type
(`(length . ,_) `(cl-incf bindat-idx 1))
(`(pack . ,args) `(bindat--pack-u8 . ,args))))
-(cl-defmethod bindat--type (op (_ (eql 'uint)) n)
+(cl-defmethod bindat--type (op (_ (eql 'uint)) n &optional le)
(if (eq n 8) (bindat--type op 'byte)
(bindat--pcase op
- ('unpack `(bindat--unpack-uint ,n))
+ ('unpack
+ `(if ,le (bindat--unpack-uintr ,n) (bindat--unpack-uint ,n)))
(`(length . ,_) `(cl-incf bindat-idx (/ ,n 8)))
- (`(pack . ,args) `(bindat--pack-uint ,n . ,args)))))
+ (`(pack . ,args)
+ `(if ,le (bindat--pack-uintr ,n . ,args)
+ (bindat--pack-uint ,n . ,args))))))
-(cl-defmethod bindat--type (op (_ (eql 'uintr)) n)
+(cl-defmethod bindat--type (op (_ (eql 'uintr)) n) ;Obsolete since Emacs-29.
(if (eq n 8) (bindat--type op 'byte)
(bindat--pcase op
('unpack `(bindat--unpack-uintr ,n))
@@ -849,8 +852,7 @@ bindat-type
"Return the Bindat type value to pack&unpack TYPE.
TYPE is a Bindat type expression. It can take the following forms:
- uint BITLEN - Big-endian unsigned integer
- uintr BITLEN - Little-endian unsigned integer
+ uint BITLEN [LE] - unsigned integer (big-endian if LE is nil)
str LEN - Byte string
strz [LEN] - Zero-terminated byte-string
bits LEN - Bit vector (LEN is counted in bytes)
@@ -935,9 +937,9 @@ bindat--make-docstring
(if ud (help-add-fundoc-usage combined-doc (car ud)) combined-doc)))))
(bindat-defmacro u8 () "Unsigned 8bit integer." '(byte))
-(bindat-defmacro sint (bitlen r)
+(bindat-defmacro sint (bitlen le)
"Signed integer of size BITLEN.
-Bigendian if R is nil and little endian if not."
+Big-endian if LE is nil and little-endian if not."
(let ((bl (make-symbol "bitlen"))
(max (make-symbol "max"))
(wrap (make-symbol "wrap")))
@@ -945,7 +947,7 @@ sint
(,max (ash 1 (1- ,bl)))
(,wrap (+ ,max ,max)))
(struct :pack-var v
- (n if ,r (uintr ,bl) (uint ,bl)
+ (n uint ,bl ,le
:pack-val (if (< v 0) (+ v ,wrap) v))
:unpack-val (if (>= n ,max) (- n ,wrap) n)))))
diff --git a/test/lisp/emacs-lisp/bindat-tests.el b/test/lisp/emacs-lisp/bindat-tests.el
index 48170727525..1ce402977f5 100644
--- a/test/lisp/emacs-lisp/bindat-tests.el
+++ b/test/lisp/emacs-lisp/bindat-tests.el
@@ -36,7 +36,7 @@ data-bindat-spec
(bindat-type
(type u8)
(opcode u8)
- (length uintr 16) ;; little endian order
+ (length uint 16 'le) ;; little endian order
(id strz 8)
(data vec length)
(_ align 4)))
@@ -128,18 +128,17 @@ bindat-test--sint
(r (zerop (% kind 2))))
(dotimes (_ 100)
(let* ((n (random (ash 1 bitlen)))
- (i (- n (ash 1 (1- bitlen)))))
+ (i (- n (ash 1 (1- bitlen))))
+ (stype (bindat-type sint bitlen r))
+ (utype (bindat-type if r (uintr bitlen) (uint bitlen))))
(should (equal (bindat-unpack
- (bindat-type sint bitlen r)
- (bindat-pack (bindat-type sint bitlen r) i))
+ stype
+ (bindat-pack stype i))
i))
(when (>= i 0)
- (should (equal (bindat-pack
- (bindat-type if r (uintr bitlen) (uint bitlen)) i)
- (bindat-pack (bindat-type sint bitlen r) i)))
- (should (equal (bindat-unpack
- (bindat-type if r (uintr bitlen) (uint bitlen))
- (bindat-pack (bindat-type sint bitlen r) i))
+ (should (equal (bindat-pack utype i)
+ (bindat-pack stype i)))
+ (should (equal (bindat-unpack utype (bindat-pack stype i))
i))))))))
(defconst bindat-test--LEB128
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