bug#7089: 23.2; slow ansi-color-apply

[Leo]

The following version fixed some glitches in setting ansi-color-context.
Also I have received an email from Alex that welcomes the improvement.
Let me know if I should send a patch in.

(defun ansi-color-apply* (string)
  "A more efficient implementation of `ansi-color-apply' (which see)."
  (let ((face (car ansi-color-context))
        start end fragment escape-sequence)
    ;; If context was saved and is a string, prepend it.
    (if (cadr ansi-color-context)
        (setq string (concat (cadr ansi-color-context) string)
              ansi-color-context nil))
    (prog1
        (with-temp-buffer
          (insert string)
          (setq start (point-min-marker))
          (goto-char start)
          (while (re-search-forward ansi-color-drop-regexp nil t)
            (replace-match ""))
          (goto-char start)
          ;; Find the next escape sequence.
          (while (re-search-forward ansi-color-regexp nil t)
            (setq end (match-beginning 0))
            (when face
              (put-text-property start end 'ansi-color t)
              (put-text-property start end 'face face))
            (setq start (copy-marker (match-end 0)))
            (setq escape-sequence (match-string 1))
            (replace-match "")
            (setq face (ansi-color-apply-sequence escape-sequence face)))
          ;; search for the possible start of a new escape sequence
          (if (re-search-forward "\033" nil t)
              (setq fragment
                    (delete-and-extract-region (match-beginning 0)
                                               (point-max))))
          ;; if the rest of the string should have a face, put it there
          (when face
            (put-text-property start (point-max) 'ansi-color t)
            (put-text-property start (point-max) 'face face))
          ;; return the string
          (buffer-string))
      ;; save context; NB: ansi-color-context is buffer-local so set it after
      ;; return to the original buffer
      (if (or face fragment)
          (setq ansi-color-context (list face fragment))
        (setq ansi-color-context nil)))))

Leo