* arith.c (atang2): New function.

* eval.c (eval_init): Register as atang2 as a atan2 intrinsic.

* lib.h (atang2): Declared.

* txr.1: Documented atan2.

4 files changed, 12 insertions, 2 deletions

diff --git a/arith.c b/arith.c
index e4972209..09828f59 100644
--- a/arith.c
+++ b/arith.c
@@ -1431,6 +1431,12 @@ val atang(val num)
   return flo(atan(c_flo(to_float(lit("atan"), num))));
 }
 
+val atang2(val y, val x)
+{
+  return flo(atan2(c_flo(to_float(lit("atan2"), y)),
+                   c_flo(to_float(lit("atan2"), x))));
+}
+
 val loga(val num)
 {
   return flo(log(c_flo(to_float(lit("log"), num))));
diff --git a/eval.c b/eval.c
index ce610dd1..6bb4b5d9 100644
--- a/eval.c
+++ b/eval.c
@@ -2361,6 +2361,7 @@ void eval_init(void)
   reg_fun(intern(lit("asin"), user_package), func_n1(asine));
   reg_fun(intern(lit("acos"), user_package), func_n1(acosi));
   reg_fun(intern(lit("atan"), user_package), func_n1(atang));
+  reg_fun(intern(lit("atan2"), user_package), func_n2(atang2));
   reg_fun(intern(lit("log"), user_package), func_n1(loga));
   reg_fun(intern(lit("exp"), user_package), func_n1(expo));
   reg_fun(intern(lit("sqrt"), user_package), func_n1(sqroot));
diff --git a/lib.h b/lib.h
index f4558bf2..d5158b64 100644
--- a/lib.h
+++ b/lib.h
@@ -479,6 +479,7 @@ val tang(val);
 val asine(val);
 val acosi(val);
 val atang(val);
+val atang2(val, val);
 val loga(val);
 val expo(val);
 val logand(val, val);
diff --git a/txr.1 b/txr.1
index df8ef0dd..42255176 100644
--- a/txr.1
+++ b/txr.1
@@ -8895,7 +8895,7 @@ If <number> an integer, it is simply returned.
 If the argument is a float, then the value returned is a float.
 For instance (floor 1.1) returns 1.0 rather than 1.
 
-.SS Functions sin, cos, tan, asin, acos, atan
+.SS Functions sin, cos, tan, asin, acos, atan, atan2
 
 .TP
 Syntax:
@@ -8904,6 +8904,7 @@ Syntax:
   (cos <radians>)
   (tan <radians>)
   (atan <slope>)
+  (atan2 <y> <x>)
   (asin <num>)
   (acos <num>)
 
@@ -8915,7 +8916,8 @@ return a float result. The sin, cos and tan functions compute the sine and
 cosine and tangent of the <radians> argument which represents an angle
 expressed in radians. The atan, acos and asin are their respective inverse
 functions.  The <num> argument to asin and acos must be in the
-range -1.0 to 1.0.
+range -1.0 to 1.0. The atan2 function converts the rectilinear coordinates
+<x>  and <y> to an angle in polar coordinates in the range [0, 2pi).
 
 .SS Functions log, exp