1 files changed, 27 insertions, 20 deletions
diff --git a/lisp/image/exif.el b/lisp/image/exif.el
index c561ea729af..503e3ffadc7 100644
--- a/lisp/image/exif.el
+++ b/lisp/image/exif.el
@@ -110,7 +110,7 @@ from the return value of this function."
     (exif-parse-buffer)))
 
 (defun exif-parse-buffer (&optional buffer)
-  "Parse BUFFER (which should be a JPEG file) and return the Exif data, if any.
+  "Parse BUFFER (which should visit a JPEG file) and return Exif data, if any.
 The return value is a list of Exif items.
 
 If the data is invalid, an `exif-error' is signaled.
@@ -134,17 +134,17 @@ from the return value of this function."
           (exif--parse-exif-chunk app1))))))
 
 (defun exif-field (field data)
-  "Return raw FIELD from EXIF.
+  "Return raw FIELD from Exif DATA.
 If FIELD is not present in the data, return nil.
 FIELD is a symbol in the cdr of `exif-tag-alist'.
-DATA is the result of calling `exif-parse-file'."
+DATA is the result of calling `exif-parse-file' or `exif-parse-buffer'."
   (plist-get (seq-find (lambda (e)
                          (eq field (plist-get e :tag-name)))
                        data)
              :value))
 
 (defun exif-orientation (exif)
-  "Return the orientation (in degrees) in EXIF.
+  "Return the orientation (in degrees) in EXIF data.
 If the orientation isn't present in the data, return nil."
   (let ((code (exif-field 'orientation exif)))
     (cadr (assq code exif--orientation))))
@@ -254,21 +254,24 @@ If the orientation isn't present in the data, return nil."
         ;; We've reached the end of the directories.
         dir))))
 
-(defun exif--direct-ascii-value (value bytes le)
-  "Make VALUE into a zero-terminated string.
-VALUE is an integer representing BYTES characters."
+(defun exif--direct-ascii-value (value nbytes le)
+  "Make a string representing VALUE with NBYTES bytes according to LE endianness.
+VALUE is an integer value of NBYTES bytes.
+The return value is a null-terminated unibyte string whose length is
+NBYTES+1 bytes.  If LE is non-nil, the returned string representation of
+VALUE is little-endian, otherwise it is big-endian."
   (with-temp-buffer
     (set-buffer-multibyte nil)
     (if le
-        (dotimes (i bytes)
+        (dotimes (i nbytes)
           (insert (logand (ash value (* i -8)) 255)))
-      (dotimes (i bytes)
-        (insert (logand (ash value (* (- (1- bytes) i) -8)) 255))))
+      (dotimes (i nbytes)
+        (insert (logand (ash value (* (- (1- nbytes) i) -8)) 255))))
     (insert 0)
     (buffer-string)))
 
 (defun exif--process-value (value type le)
-  "Do type-based post-processing of the value."
+  "Do type-based post-processing of the VALUE whose endianness is per LE."
   (cl-case type
     ;; Chop off trailing zero byte.
     (ascii (substring value 0 (1- (length value))))
@@ -281,7 +284,8 @@ VALUE is an integer representing BYTES characters."
     (otherwise value)))
 
 (defun exif--read-chunk (bytes)
-  "Return BYTES octets from the buffer and advance point that much."
+  "Return BYTES octets from the current buffer and advance point that much.
+This function assumes that the current buffer is unibyte."
   (when (> (+ (point) bytes) (point-max))
     (signal 'exif-error "Premature end of file"))
   (prog1
@@ -289,8 +293,9 @@ VALUE is an integer representing BYTES characters."
     (forward-char bytes)))
 
 (defun exif--read-number-be (bytes)
-  "Read BYTES octets from the buffer as a chunk of big-endian bytes.
-Advance point to after the read bytes."
+  "Read BYTES octets from the current buffer as a chunk of big-endian bytes.
+Advance point to after the read bytes.
+This function assumes that the current buffer is unibyte."
   (when (> (+ (point) bytes) (point-max))
     (signal 'exif-error "Premature end of file"))
   (let ((sum 0))
@@ -300,8 +305,9 @@ Advance point to after the read bytes."
     sum))
 
 (defun exif--read-number-le (bytes)
-  "Read BYTES octets from the buffer as a chunk of low-endian bytes.
-Advance point to after the read bytes."
+  "Read BYTES octets from the current buffer as a chunk of little-endian bytes.
+Advance point to after the read bytes.
+This function assumes that the current buffer is unibyte."
   (when (> (+ (point) bytes) (point-max))
     (signal 'exif-error "Premature end of file"))
   (let ((sum 0))
@@ -310,10 +316,11 @@ Advance point to after the read bytes."
       (forward-char 1))
     sum))
 
-(defun exif--read-number (bytes lower-endian)
-  "Read BYTES octets from the buffer with endianness determined by LOWER-ENDIAN.
-Advance point to after the read bytes."
-  (if lower-endian
+(defun exif--read-number (bytes little-endian)
+  "Read BYTES octets from current buffer with endianness given by LITTLE-ENDIAN.
+Advance point to after the read bytes.
+This function assumes that the current buffer is unibyte."
+  (if little-endian
       (exif--read-number-le bytes)
     (exif--read-number-be bytes)))