base,arch-sparc: Overhaul the small fenv wrapper in base.

This was written in C, broke the style guide, used macros, used an
obsolete m5_ prefix, and used extern "C" in an odd way.

Change-Id: If38f9a1bca6fd4a4f7f533ddb1e81d6207bc9c44
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40878
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/sparc/isa/formats/basic.isa

@@ -156,19 +156,27 @@ def format FpBasic(code, *flags) {{
     exec_code = """
     Fsr |= bits(Fsr, 4, 0) << 5;
     Fsr = insertBits(Fsr, 4, 0, 0);
-    int newrnd = M5_FE_TONEAREST;
+    gem5::RoundingMode newrnd = gem5::RoundingMode::ToNearest;
     switch (Fsr<31:30>) {
-      case 0: newrnd = M5_FE_TONEAREST; break;
-      case 1: newrnd = M5_FE_TOWARDZERO; break;
-      case 2: newrnd = M5_FE_UPWARD; break;
-      case 3: newrnd = M5_FE_DOWNWARD; break;
+      case 0:
+        newrnd = gem5::RoundingMode::ToNearest;
+        break;
+      case 1:
+        newrnd = gem5::RoundingMode::TowardZero;
+        break;
+      case 2:
+        newrnd = gem5::RoundingMode::Upward;
+        break;
+      case 3:
+        newrnd = gem5::RoundingMode::Downward;
+        break;
     }
-    int oldrnd = m5_fegetround();
-    m5_fesetround(newrnd);
+    gem5::RoundingMode oldrnd = gem5::getFpRound();
+    gem5::setFpRound(newrnd);
     __asm__ __volatile__("" ::: "memory");
     fault = doFpOp(xc, traceData);
     __asm__ __volatile__("" ::: "memory");
-    m5_fesetround(oldrnd);
+    gem5::setFpRound(oldrnd);
     return fault;
 """
     fp_code = filterDoubles(code)

src/base/SConscript

@@ -43,7 +43,7 @@ Executable('cprintftime', 'cprintftime.cc', 'cprintf.cc')
 Source('debug.cc')
 GTest('debug.test', 'debug.test.cc', 'debug.cc')
 if env['USE_FENV']:
-    Source('fenv.c')
+    Source('fenv.cc')
 else:
     warning("No IEEE FP rounding mode control.\n"
             "FP results may deviate slightly from other platforms.")

src/base/fenv.cc

@@ -1,4 +1,5 @@
 /*
+ * Copyright 2021 Google Inc.
  * Copyright (c) 2007 The Regents of The University of Michigan
  * All rights reserved.
  *
@@ -26,29 +27,28 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <assert.h>
+#include "base/fenv.hh"
+
 #include <fenv.h>
-#include <stdlib.h>
 
-void m5_fesetround(int rm);
-int m5_fegetround();
+#include <cstdlib>
 
-static const int m5_round_ops[] =  {FE_DOWNWARD, FE_TONEAREST, FE_TOWARDZERO, FE_UPWARD};
-
-void m5_fesetround(int rm)
+namespace gem5
 {
-    assert(rm >= 0 && rm < 4);
-    fesetround(m5_round_ops[rm]);
-}
 
-int m5_fegetround()
+static const int roundOps[] =
+    { FE_DOWNWARD, FE_TONEAREST, FE_TOWARDZERO, FE_UPWARD };
+
+void setFpRound(RoundingMode rm) { fesetround(roundOps[(int)rm]); }
+
+RoundingMode
+getFpRound()
 {
-    int x;
     int rm = fegetround();
-    for (x = 0; x < 4; x++)
-        if (m5_round_ops[x] == rm)
-            return x;
+    for (int x = 0; x < 4; x++)
+        if (roundOps[x] == rm)
+            return (RoundingMode)x;
     abort();
-    return 0;
 }
 
+} // namespace gem5

src/base/fenv.hh

@@ -31,23 +31,34 @@
 
 #include "config/use_fenv.hh"
 
-#define M5_FE_DOWNWARD     0
-#define M5_FE_TONEAREST    1
-#define M5_FE_TOWARDZERO   2
-#define M5_FE_UPWARD       3
+namespace gem5
+{
+
+enum class RoundingMode
+{
+    Downward = 0,
+    ToNearest = 1,
+    TowardZero = 2,
+    Upward = 3
+};
 
 #if USE_FENV
-extern "C" {
-void m5_fesetround(int rm);
-int m5_fegetround();
-}
+
+void setFpRound(RoundingMode rm);
+RoundingMode getFpRound();
+
 #else
 
 // Dummy definitions to allow code to compile w/o a real <fenv.h>.
-inline void m5_fesetround(int rm) { ; }
-inline int m5_fegetround() {return 0; }
+static inline void setFpRound(RoundingMode rm) {}
+static inline
+RoundingMode getFpRound()
+{
+    return RoundingMode::Downward;
+}
 
 #endif // USE_FENV
 
+} // namespace gem5
 
 #endif // __BASE_FENV_HH__