suzanne.soy/racket
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

atan: exception on exact 0+1i or 0-1i, exact 0 on positive x

Browse Source 
Change from treating exact 0+1i and 0-1i like the corresponding
inexact values.

Also, change from treating `(atan 0 x)` as exact 0 only when x is
exact. That's consistent with `angle` producing exact 0 for a positive
real number.
This commit is contained in:
Matthew Flatt 2019-01-17 19:57:22 -07:00
parent f27c9330a5
commit 422d5579b3
3 changed files with 31 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
pkgs/racket-doc/scribblings/reference/numbers.scrbl
View File

@ -704,7 +704,8 @@ Returns the arccosine in radians of @racket[z].
In the one-argument case, returns the arctangent of the inexact
approximation of @racket[z], except that the result is an exact
@racket[0] for an exact @racket[0] argument.
@racket[0] for @racket[z] as @racket[0], and the @exnraise[exn:fail:contract:divide-by-zero]
for @racket[z] as exact @racket[0+1i] or exact @racket[0-1i].
In the two-argument case, the result is roughly the same as @racket[
(atan (/ (exact->inexact y)) (exact->inexact x))], but the signs of @racket[y]
@ -712,11 +713,15 @@ In the two-argument case, the result is roughly the same as @racket[
suitable angle is returned when @racket[y] divided by @racket[x]
produces @racket[+nan.0] in the case that neither @racket[y] nor
@racket[x] is @racket[+nan.0]. Finally, if @racket[y] is exact
@racket[0] and @racket[x] is an exact positive number, the result is
@racket[0] and @racket[x] is a positive number, the result is
exact @racket[0]. If both @racket[x] and @racket[y] are exact
@racket[0], the @exnraise[exn:fail:contract:divide-by-zero].
@mz-examples[(atan 0.5) (atan 2 1) (atan -2 -1) (atan 1+05.i) (atan +inf.0 -inf.0)]}
@mz-examples[(atan 0.5) (atan 2 1) (atan -2 -1) (atan 1+05.i) (atan +inf.0 -inf.0)]
@history[#:changed "7.2.0.2" @elem{Changed to raise @racket[exn:fail:contract:divide-by-zero]
for @racket[0+1i] and @racket[0-1i] and to produce exact @racket[0]
for any positive @racket[x] (not just exact values) when @racket[y] is @racket[0].}]}
@; ------------------------------------------------------------------------
@subsection{Complex Numbers}

8
pkgs/racket-test-core/tests/racket/number.rktl
View File

@ -1669,8 +1669,6 @@
(test pi angle (- big-num))
(test pi angle -3/4)
(test pi angle -3+0.0i))
(test -inf.0 atan 0+i)
(test -inf.0 atan 0-i)
(err/rt-test (angle 'a))
(err/rt-test (angle 0) exn:fail:contract:divide-by-zero?)
@ -2098,9 +2096,13 @@
(test 0 atan 0 1)
(test 0 atan 0 (expt 2 100))
(test 0 atan 0 5/2)
(test 0.0 atan 0 1.0)
(test 0 atan 0 1.0)
(test 314.0 round (* 100 (atan 0 -1)))
(err/rt-test (atan 0 0) exn:fail:contract:divide-by-zero?)
(err/rt-test (atan 0+i) exn:fail:contract:divide-by-zero?)
(err/rt-test (atan 0-i) exn:fail:contract:divide-by-zero?)
(test -inf.0 atan 0+1.0i)
(test -inf.0 atan 0-1.0i)
(test 1024.0 round (expt 2.0 10.0))
(test 1024.0 round (expt -2.0 10.0))
(test -512.0 round (expt -2.0 9.0))

23
racket/src/racket/src/number.c
View File

@ -2913,8 +2913,23 @@ static Scheme_Object *complex_atan(Scheme_Object *c)
{
Scheme_Object *one_half = NULL;
if (scheme_complex_eq(c, scheme_plus_i) || scheme_complex_eq(c, scheme_minus_i))
return scheme_minus_inf_object;
if (SAME_OBJ(_scheme_complex_real_part(c), scheme_make_integer(0))) {
Scheme_Object *i = _scheme_complex_imaginary_part(c);
if (SAME_OBJ(i, scheme_make_integer(1)) || SAME_OBJ(i, scheme_make_integer(-1))) {
scheme_raise_exn(MZEXN_FAIL_CONTRACT_DIVIDE_BY_ZERO, "atan: undefined for %V", c);
return NULL;
#ifdef MZ_USE_SINGLE_FLOATS
} else if (SCHEME_FLTP(i)) {
float f = SCHEME_FLT_VAL(i);
if ((f == 1.0) || (f == -1.0))
return scheme_single_minus_inf_object;
#endif
} else if (SCHEME_DBLP(i)) {
double d = SCHEME_DBL_VAL(i);
if ((d == 1.0) || (d == -1.0))
return scheme_minus_inf_object;
}
}
/* select single versus complex: */
#ifdef MZ_USE_SINGLE_FLOATS
@ -3115,9 +3130,7 @@ atan_prim (int argc, Scheme_Object *argv[])
"atan: undefined for 0 and 0");
ESCAPED_BEFORE_HERE;
}
if ((SCHEME_INTP(n2) && (SCHEME_INT_VAL(n2) > 0))
|| (SCHEME_BIGNUMP(n2) && (SCHEME_BIGPOS(n2)))
|| (SCHEME_RATIONALP(n2) && scheme_is_positive(n2)))
if (!SCHEME_COMPLEXP(n2) && scheme_is_positive(n2))
return zeroi;
}