[Qemu-devel] [PATCH] target/ppc: bcdsub fix sign when result is zero

[Yasmin Beatriz <yasmins@linux.ibm.com>]

When the result of bcdsub is equal to zero, the result sign may be
set to negative in some cases, and this does not follow the Power ISA
specifications as to decimal integer arithmetic instructions.

Signed-off-by: Yasmin Beatriz <yasmins@linux.ibm.com>
---
 target/ppc/int_helper.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/target/ppc/int_helper.c b/target/ppc/int_helper.c
index 03d37da..fa18e6e 100644
--- a/target/ppc/int_helper.c
+++ b/target/ppc/int_helper.c
@@ -2747,6 +2747,9 @@ uint32_t helper_bcdadd(ppc_avr_t *r,  ppc_avr_t *a, ppc_avr_t *b, uint32_t ps)
             result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(sgna, ps);
             zero = bcd_sub_mag(&result, a, b, &invalid, &overflow);
             cr = (sgna > 0) ? CRF_GT : CRF_LT;
+        } else if (bcd_cmp_mag(a, b) == 0) {
+            result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(0, ps);
+            zero = bcd_sub_mag(&result, b, a, &invalid, &overflow);
         } else {
             result.u8[BCD_DIG_BYTE(0)] = bcd_preferred_sgn(sgnb, ps);
             zero = bcd_sub_mag(&result, b, a, &invalid, &overflow);
-- 
1.8.3.1