commit c02c71187c9794b50444e2858c582e66a3442ee8
author Ian Lance Taylor <iant@golang.org> Mon Feb 05 11:23:41 2018 -0800
committer Ian Lance Taylor <iant@golang.org> Mon Feb 05 19:25:10 2018 +0000
tree cecc275b17e4057a564317d90e582c5cb25da87f
parent 7eebd495df915ab87926b8dd88f554674cfdacea

compiler: rollback "avoid negative zero in float constants"

It uses functions that are not available in MPFR 2.4.2, which is the
current version supported by GCC.

Original change description:

    compiler: avoid negative zero in float constants

    Check for negative numbers with very small magnitudes that will round
    to negative zero, and force them to positive zero instead.

    This implements the spec clarification in https://golang.org/cl/14727.
    The test is in https://golang.org/cl/91895.

    Fixes golang/go#12621

Updates golang/go#12621

Change-Id: Ibe89ba756c044bef7796934dbb01550db041dced
Reviewed-on: https://go-review.googlesource.com/92055
Reviewed-by: Ian Lance Taylor <iant@golang.org>

go/expressions.cc

diff --git a/go/expressions.cc b/go/expressions.cc
index 03f8c68..8555c05 100644
--- a/go/expressions.cc
+++ b/go/expressions.cc
@@ -16158,16 +16158,10 @@
   this->clear();
   this->classification_ = NC_FLOAT;
   this->type_ = type;
-
   // Numeric constants do not have negative zero values, so remove
   // them here.  They also don't have infinity or NaN values, but we
   // should never see them here.
-  int bits = 0;
-  if (type != NULL
-      && type->float_type() != NULL
-      && !type->float_type()->is_abstract())
-    bits = type->float_type()->bits();
-  if (Numeric_constant::is_float_zero(val, bits))
+  if (mpfr_zero_p(val))
     mpfr_init_set_ui(this->u_.float_val, 0, GMP_RNDN);
   else
     mpfr_init_set(this->u_.float_val, val, GMP_RNDN);
@@ -16181,50 +16175,8 @@
   this->clear();
   this->classification_ = NC_COMPLEX;
   this->type_ = type;
-
-  // Avoid negative zero as in set_float.
-  int bits = 0;
-  if (type != NULL
-      && type->complex_type() != NULL
-      && !type->complex_type()->is_abstract())
-    bits = type->complex_type()->bits() / 2;
-
-  mpfr_t real;
-  mpfr_init_set(real, mpc_realref(val), GMP_RNDN);
-  if (Numeric_constant::is_float_zero(real, bits))
-    mpfr_set_ui(real, 0, GMP_RNDN);
-
-  mpfr_t imag;
-  mpfr_init_set(imag, mpc_imagref(val), GMP_RNDN);
-  if (Numeric_constant::is_float_zero(imag, bits))
-    mpfr_set_ui(imag, 0, GMP_RNDN);
-
   mpc_init2(this->u_.complex_val, mpc_precision);
-  mpc_set_fr_fr(this->u_.complex_val, real, imag, MPC_RNDNN);
-
-  mpfr_clear(real);
-  mpfr_clear(imag);
-}
-
-// Return whether VAL, at a precision of BITS, is zero.  BITS may be
-// zero in which case it is ignored.
-
-bool
-Numeric_constant::is_float_zero(const mpfr_t val, int bits)
-{
-  if (mpfr_zero_p(val))
-    return true;
-  switch (bits)
-    {
-    case 0:
-      return false;
-    case 32:
-      return mpfr_get_flt(val, GMP_RNDN) == 0;
-    case 64:
-      return mpfr_get_d(val, GMP_RNDN) == 0;
-    default:
-      go_unreachable();
-    }
+  mpc_set(this->u_.complex_val, val, MPC_RNDNN);
 }
 
 // Get an int value.

go/expressions.h

diff --git a/go/expressions.h b/go/expressions.h
index 3acaeb2..d16a284 100644
--- a/go/expressions.h
+++ b/go/expressions.h
@@ -4220,9 +4220,6 @@
   bool
   check_complex_type(Complex_type*, bool, Location);
 
-  static bool
-  is_float_zero(const mpfr_t, int bits);
-
   // The kinds of constants.
   enum Classification
   {