alpha: Streamline __setfpucw

The convert_bit macro allows the compiler to translate the bit
positions more efficiently.  The assumption of only running at
program startup allows eliding the __ieee_get_fp_control call.

2 files changed, 38 insertions, 53 deletions

diff --git a/ports/ChangeLog.alpha b/ports/ChangeLog.alpha
index d00b1e968b..ab807f7d47 100644
--- a/ports/ChangeLog.alpha
+++ b/ports/ChangeLog.alpha
@@ -1,5 +1,8 @@
 2012-12-13  Richard Henderson  <rth@redhat.com>
 
+	* sysdeps/unix/sysv/linux/alpha/setfpucw.c (__setfpucw): Rewrite
+	with the assumption of being used at program startup only.
+
 	* sysdeps/unix/sysv/linux/alpha/nptl/localplt.data: Add optional
 	entries for _OtsConvertFloatTX, _OtsCvtQUX, _OtsCvtXQ, _OtsGtrX,
 	_OtsLeqX, _OtsNintXQ.
diff --git a/ports/sysdeps/unix/sysv/linux/alpha/setfpucw.c b/ports/sysdeps/unix/sysv/linux/alpha/setfpucw.c
index becc11f94c..99ffd06fad 100644
--- a/ports/sysdeps/unix/sysv/linux/alpha/setfpucw.c
+++ b/ports/sysdeps/unix/sysv/linux/alpha/setfpucw.c
@@ -1,5 +1,5 @@
 /* Set FP exception mask and rounding mode.
-   Copyright (C) 1996, 1997, 1998, 2003 Free Software Foundation, Inc.
+   Copyright (C) 1996-2012 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -17,63 +17,45 @@
    <http://www.gnu.org/licenses/>.  */
 
 #include <fpu_control.h>
-#include <asm/fpu.h>
+#include <fenv_libc.h>
 
-extern void		__ieee_set_fp_control (unsigned long);
-libc_hidden_proto(__ieee_set_fp_control)
 
-extern unsigned long	__ieee_get_fp_control (void);
-libc_hidden_proto(__ieee_get_fp_control)
-
-static inline unsigned long
-rdfpcr (void)
-{
-  unsigned long fpcr;
-  asm ("excb; mf_fpcr %0" : "=f"(fpcr));
-  return fpcr;
-}
-
-
-static inline void
-wrfpcr (unsigned long fpcr)
-{
-  asm volatile ("mt_fpcr %0; excb" : : "f"(fpcr));
-}
+#define convert_bit(M, F, T)		\
+    ((T) < (F)				\
+     ? ((M) / ((F) / (T))) & (T)	\
+     : ((M) & (F)) * ((T) / (F)))
 
 
 void
 __setfpucw (fpu_control_t fpu_control)
 {
-  unsigned long fpcr = 0, fpcw = 0;
-
-  if (!fpu_control)
-    fpu_control = _FPU_DEFAULT;
-
-  /* first, set dynamic rounding mode: */
-
-  fpcr = rdfpcr();
-  fpcr &= ~FPCR_DYN_MASK;
-  switch (fpu_control & 0xc00)
-    {
-    case _FPU_RC_NEAREST:	fpcr |= FPCR_DYN_NORMAL; break;
-    case _FPU_RC_DOWN:		fpcr |= FPCR_DYN_MINUS; break;
-    case _FPU_RC_UP:		fpcr |= FPCR_DYN_PLUS; break;
-    case _FPU_RC_ZERO:		fpcr |= FPCR_DYN_CHOPPED; break;
-    }
-  wrfpcr(fpcr);
-
-  /* now tell kernel about traps that we like to hear about: */
-
-  fpcw = __ieee_get_fp_control();
-  fpcw &= ~IEEE_TRAP_ENABLE_MASK;
-
-  if (!(fpu_control & _FPU_MASK_IM)) fpcw |= IEEE_TRAP_ENABLE_INV;
-  if (!(fpu_control & _FPU_MASK_DM)) fpcw |= IEEE_TRAP_ENABLE_UNF;
-  if (!(fpu_control & _FPU_MASK_ZM)) fpcw |= IEEE_TRAP_ENABLE_DZE;
-  if (!(fpu_control & _FPU_MASK_OM)) fpcw |= IEEE_TRAP_ENABLE_OVF;
-  if (!(fpu_control & _FPU_MASK_PM)) fpcw |= IEEE_TRAP_ENABLE_INE;
-
-  __fpu_control = fpu_control;	/* update global copy */
-
-  __ieee_set_fp_control(fpcw);
+  unsigned long fpcr, swcr, fc = (int)fpu_control;
+
+  /* ??? If this was a real external interface we'd want to read the current
+     exception state with __ieee_get_fp_control.  But this is an internal
+     function only called at process startup, so there's no point in trying
+     to preserve exceptions that cannot have been raised yet.  Indeed, this
+     entire function is likely to be one big nop unless the user overrides
+     the default __fpu_control variable.  */
+
+  /* Convert the rounding mode from fpu_control.h format.  */
+  const unsigned long conv_rnd
+    = (  (FE_TOWARDZERO << (_FPU_RC_ZERO >> 8))
+       | (FE_DOWNWARD << (_FPU_RC_DOWN >> 8))
+       | (FE_TONEAREST << (_FPU_RC_NEAREST >> 8))
+       | (FE_UPWARD << (_FPU_RC_UP >> 8)));
+
+  fpcr = ((conv_rnd >> ((fc >> 8) & 3)) & 3) << FPCR_ROUND_SHIFT;
+
+  /* Convert the exception mask from fpu_control.h format.  */
+  swcr  = convert_bit (~fc, _FPU_MASK_IM, FE_INVALID >> SWCR_ENABLE_SHIFT);
+  swcr |= convert_bit (~fc, _FPU_MASK_DM, FE_UNDERFLOW >> SWCR_ENABLE_SHIFT);
+  swcr |= convert_bit (~fc, _FPU_MASK_ZM, FE_DIVBYZERO >> SWCR_ENABLE_SHIFT);
+  swcr |= convert_bit (~fc, _FPU_MASK_OM, FE_OVERFLOW >> SWCR_ENABLE_SHIFT);
+  swcr |= convert_bit (~fc, _FPU_MASK_PM, FE_INEXACT >> SWCR_ENABLE_SHIFT);
+
+  /* Install everything.  */
+  __fpu_control = fc;
+  asm volatile ("mt_fpcr %0" : : "f"(fpcr));
+  __ieee_set_fp_control(swcr);
 }