|
Has anyone else worked on exercise 13.3(b) in "ANSI Common Lisp"? I approached it by declaring all the variables in Figure 9.2 as long-floats: ; Use declarations in math utilities:
(defun sq (x)
(declare (long-float x))
(* x x))
(defun mag (x y z)
(declare (long-float x y z))
(sqrt (+ (sq x) (sq y) (sq z))))
(defun unit-vector (x y z)
(declare (long-float x y z))
(let ((d (mag x y z)))
(declare (long-float d))
(values (/ x d) (/ y d) (/ z d))))
(defstruct (point (:conc-name nil))
x y z)
(defun distance (p1 p2)
(mag (- (x p1) (x p2))
(- (y p1) (y p2))
(- (z p1) (z p2))))
(defun minroot (a b c)
(declare (long-float a b c))
(if (zerop a)
(/ (- c) b)
(let ((disc (- (sq b) (* 4 a c))))
(declare (long-float disc))
(unless (minusp disc)
(let ((discrt (sqrt disc)))
(declare (long-float discrt))
(min (/ (+ (- b) discrt) (* 2 a))
(/ (- (- b) discrt) (* 2 a))))))))
However, the running time slowed down as a result of this change, rather than sped up.Note that I used long-floats, rather than double-floats, because, when I used double-floats, the output was slightly different (only off by 1 on some values) than the original version in which variables were undeclared. However, the output was slightly different with long-floats, too, so I guess that didn't help. Anyway, should declaring these variables make the program faster, or am I doing the problem incorrectly? And why is the output slightly different if I'm using the largest size floating-points? Below is the diff: diff "spheres.pgm copy" spheres.pgm
125c125
< 62
---
> 61
179c179
< 62
---
> 61
6837,6838c6837,6838
< 41
< 117
---
> 42
> 118
6866,6867c6866,6867
< 117
< 41
---
> 118
> 42
7028c7028
< 22
---
> 23
7076c7076
< 22
---
> 23
7138c7138
< 114
---
> 113
7166c7166
< 114
---
> 113
7226c7226
< 118
---
> 117
7278c7278
< 118
---
> 117
7416,7417c7416,7417
< 85
< 54
---
> 84
> 53
7434c7434
< 85
---
> 86
7470c7470
< 85
---
> 86
7487,7488c7487,7488
< 54
< 85
---
> 53
> 84
7531c7531
< 19
---
> 18
7539c7539
< 18
---
> 19
7565c7565
< 18
---
> 19
7573c7573
< 19
---
> 18
7831c7831
< 117
---
> 116
7873c7873
< 117
---
> 116
7937c7937
< 19
---
> 18
7967c7967
< 19
---
> 18
8006c8006
< 107
---
> 108
8008c8008
< 128
---
> 127
8018c8018
< 24
---
> 23
8086c8086
< 24
---
> 23
8096c8096
< 128
---
> 127
8098c8098
< 107
---
> 108
8152c8152
< 164
---
> 163
8707c8707
< 110
---
> 111
8797c8797
< 110
---
> 111
|