;; Pathological case, both seem to be quadratic in the length of a whitespace sequence.
(benchmark 1 `(string-match "[\s\t]+$" ,(concat (make-string 1000 ?\s) "X")))"Elapsed time: 0.090000s"
(benchmark 1 `(string-match "[\s\t]+$" ,(concat (make-string 2000 ?\s) "X")))"Elapsed time: 0.258000s"
(benchmark 1 `(string-match "[\s\t]+$" ,(concat (make-string 4000 ?\s) "X")))"Elapsed time: 0.630000s"
(benchmark 1 `(string-match "[\s\t]+$" ,(concat (make-string 8000 ?\s) "X")))"Elapsed time: 2.260000s"
(benchmark 1 `(string-match "[\s\t]+$" ,(concat (make-string 16000 ?\s) "X")))"Elapsed time: 9.306000s"

(benchmark 1 `(string-match "\\s-+$" ,(concat (make-string 1000 ?\s) "X")))"Elapsed time: 0.395000s"
(benchmark 1 `(string-match "\\s-+$" ,(concat (make-string 2000 ?\s) "X")))"Elapsed time: 0.347000s"
(benchmark 1 `(string-match "\\s-+$" ,(concat (make-string 4000 ?\s) "X")))"Elapsed time: 1.282000s"
(benchmark 1 `(string-match "\\s-+$" ,(concat (make-string 8000 ?\s) "X")))"Elapsed time: 5.051000s"
(benchmark 1 `(string-match "\\s-+$" ,(concat (make-string 16000 ?\s) "X")))"Elapsed time: 20.144000s"

;; Normal case, linear.
(benchmark 1 `(string-match "[\s\t]+$" ,(concat (make-string 8000 ?_) "X")))"Elapsed time: 0.001000s"
(benchmark 1 `(string-match "[\s\t]+$" ,(concat (make-string 16000 ?_) "X")))"Elapsed time: 0.002000s"
(benchmark 1 `(string-match "[\s\t]+$" ,(concat (make-string 32000 ?_) "X")))"Elapsed time: 0.003000s"
(benchmark 1 `(string-match "[\s\t]+$" ,(concat (make-string 64000 ?_) "X")))"Elapsed time: 0.007000s"

(benchmark 1 `(string-match "\\s-+$" ,(concat (make-string 8000 ?_) "X")))"Elapsed time: 0.004000s"
(benchmark 1 `(string-match "\\s-+$" ,(concat (make-string 16000 ?_) "X")))"Elapsed time: 0.008000s"
(benchmark 1 `(string-match "\\s-+$" ,(concat (make-string 32000 ?_) "X")))"Elapsed time: 0.016000s"
(benchmark 1 `(string-match "\\s-+$" ,(concat (make-string 64000 ?_) "X")))"Elapsed time: 0.031000s"