softfpu: Add float_round_to_odd_inf

For Arm BFDOT and BFMMLA, we need a version of round-to-odd
that overflows to infinity, instead of the max normal number.

Cc: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210525225817.400336-6-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

fpu/softfloat-parts.c.inc

@@ -176,13 +176,12 @@ static void partsN(uncanon)(FloatPartsN *p, float_status *s,
         g_assert_not_reached();
     }
 
+    overflow_norm = false;
     switch (s->float_rounding_mode) {
     case float_round_nearest_even:
-        overflow_norm = false;
         inc = ((p->frac_lo & roundeven_mask) != frac_lsbm1 ? frac_lsbm1 : 0);
         break;
     case float_round_ties_away:
-        overflow_norm = false;
         inc = frac_lsbm1;
         break;
     case float_round_to_zero:
@@ -199,6 +198,8 @@ static void partsN(uncanon)(FloatPartsN *p, float_status *s,
         break;
     case float_round_to_odd:
         overflow_norm = true;
+        /* fall through */
+    case float_round_to_odd_inf:
         inc = p->frac_lo & frac_lsb ? 0 : round_mask;
         break;
     default:
@@ -259,6 +260,7 @@ static void partsN(uncanon)(FloatPartsN *p, float_status *s,
                        ? frac_lsbm1 : 0);
                 break;
             case float_round_to_odd:
+            case float_round_to_odd_inf:
                 inc = p->frac_lo & frac_lsb ? 0 : round_mask;
                 break;
             default:

include/fpu/softfloat-types.h

@@ -134,8 +134,10 @@ typedef enum __attribute__((__packed__)) {
     float_round_up           = 2,
     float_round_to_zero      = 3,
     float_round_ties_away    = 4,
-    /* Not an IEEE rounding mode: round to the closest odd mantissa value */
+    /* Not an IEEE rounding mode: round to closest odd, overflow to max */
     float_round_to_odd       = 5,
+    /* Not an IEEE rounding mode: round to closest odd, overflow to inf */
+    float_round_to_odd_inf   = 6,
 } FloatRoundMode;
 
 /*