[Qemu-devel] [PATCH] Implement Fraction Rounded bit in FPSCR for PowerPC

[John Arbuckle <programmingkidx@gmail.com>]

Implement the PowerPC floating point status and control register flag Fraction Rounded.

Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
---
 fpu/softfloat.c               | 15 ++++++++++++---
 include/fpu/softfloat-types.h |  1 +
 target/ppc/fpu_helper.c       |  4 ++++
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 2ba36ec370..ac34f6a2de 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -702,7 +702,7 @@ static FloatParts round_canonical(FloatParts p, float_status *s,
     const uint64_t roundeven_mask = parm->roundeven_mask;
     const int exp_max = parm->exp_max;
     const int frac_shift = parm->frac_shift;
-    uint64_t frac, inc;
+    uint64_t frac, inc, rounded;
     int exp, flags = 0;
     bool overflow_norm;
 
@@ -744,7 +744,12 @@ static FloatParts round_canonical(FloatParts p, float_status *s,
         if (likely(exp > 0)) {
             if (frac & round_mask) {
                 flags |= float_flag_inexact;
-                frac += inc;
+                rounded = frac + inc;
+                if ((rounded ^ frac) & frac_lsb) {
+                    flags |= float_flag_rounded;
+                }
+                frac = rounded;
+
                 if (frac & DECOMPOSED_OVERFLOW_BIT) {
                     frac >>= 1;
                     exp++;
@@ -793,7 +798,11 @@ static FloatParts round_canonical(FloatParts p, float_status *s,
                     break;
                 }
                 flags |= float_flag_inexact;
-                frac += inc;
+                rounded = frac + inc;
+                if ((rounded ^ frac) & frac_lsb) {
+                    flags |= float_flag_rounded;
+                }
+                frac = rounded;
             }
 
             exp = (frac & DECOMPOSED_IMPLICIT_BIT ? 1 : 0);
diff --git a/include/fpu/softfloat-types.h b/include/fpu/softfloat-types.h
index 2aae6a89b1..bee576e0fd 100644
--- a/include/fpu/softfloat-types.h
+++ b/include/fpu/softfloat-types.h
@@ -147,6 +147,7 @@ enum {
 
 enum {
     float_flag_invalid   =  1,
+    float_flag_rounded   =  2,
     float_flag_divbyzero =  4,
     float_flag_overflow  =  8,
     float_flag_underflow = 16,
diff --git a/target/ppc/fpu_helper.c b/target/ppc/fpu_helper.c
index 0b7308f539..0baf1ce8e4 100644
--- a/target/ppc/fpu_helper.c
+++ b/target/ppc/fpu_helper.c
@@ -630,6 +630,10 @@ static void do_float_check_status(CPUPPCState *env, uintptr_t raddr)
         env->fpscr &= ~(1 << FPSCR_FI); /* clear the FPSCR[FI] bit */
     }
 
+    /* Set or clear the Fraction Rounded bit */
+    env->fpscr = deposit32(env->fpscr, FPSCR_FR, 1,
+                           (status & float_flag_rounded) != 0);
+
     if (cs->exception_index == POWERPC_EXCP_PROGRAM &&
         (env->error_code & POWERPC_EXCP_FP)) {
         /* Differred floating-point exception after target FPR update */
-- 
2.14.3 (Apple Git-98)