[tan.dat] added one more corner case, which should give a 100% coverage

git-svn-id: svn://scm.gforge.inria.fr/svn/mpc/trunk@319 211d60ee-9f03-0410-a15a-8952a2c7a4e4

2 files changed, 9 insertions, 5 deletions

diff --git a/src/tan.c b/src/tan.c
index 8538391..45571c9 100644
--- a/src/tan.c
+++ b/src/tan.c
@@ -206,16 +206,17 @@ mpc_tan (mpc_ptr rop, mpc_srcptr op, mpc_rnd_t rnd)
 
       /* some parts of the quotient may be exact */
       inex = mpc_div (x, x, y, MPC_RNDZZ);
-      /* OP is no pure real nor pure imaginary, so the real and imaginary
-         parts of its tangent cannot be null. */
-      /* This part of code is apparently never reached; AE */
-#if 1 /* PZ: I agree, but until we prove it is never reached, let's keep it. */
+      /* OP is no pure real nor pure imaginary, so in theory the real and
+         imaginary parts of its tangent cannot be null. However due to
+         rouding errors this might happen. Consider for example
+         tan(1+14*I) = 1.26e-10 + 1.00*I. For small precision sin(op) and
+         cos(op) differ only by a factor I, thus after mpc_div x = I and
+         its real part is zero. */
       if (mpfr_zero_p (MPC_RE (x)) || mpfr_zero_p (MPC_IM (x)))
         {
           err = prec; /* double precision */
           continue;
         }
-#endif
       if (MPC_INEX_RE (inex))
         mpfr_signbit (MPC_RE (x)) ?
           mpfr_nextbelow (MPC_RE (x)) : mpfr_nextabove (MPC_RE (x));
diff --git a/tests/tan.dat b/tests/tan.dat
index 30b9f8a..dfc93ca 100644
--- a/tests/tan.dat
+++ b/tests/tan.dat
@@ -121,3 +121,6 @@
 # yet another absurd case: op = atan (2^200) + 2^(-200000)*I;
 # expensive to compute
 # 50 0x1@50 50 0x1@-49900  1000 0x1.921fb54442d18469898cc51701b839a252049c1114cf98e803177d4c76273644a29410f31c6809bbdf2a33679a748636605614dbe4be286e9fc26adadaa3848bc90b6aecc4bcfd8de8988628a1c5302b6d540ec33d62c53131c62d4c0a6894a0b2939d784deb9521e7a621f92f1e0bd0d9564ec6981cd3608709e5c18e 1000 0x1@-50000 N N
+
+# corner case
+9 -0x9bp-51 9 -1    9 -0x16dp-8 9 -0x77p-3   N N