[PATCH v2 4/4] target/m68k: fix FPSR quotient byte for frem instruction

[Mark Cave-Ayland]

The FPSR quotient byte should be set to the value of the quotient and not the
result. Manually calculate the quotient in the frem helper in round to nearest
even mode (note this is different from the quotient calculated internally for
fmod), and use it to set the quotient byte accordingly.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1314
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
---
 target/m68k/fpu_helper.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/target/m68k/fpu_helper.c b/target/m68k/fpu_helper.c
index 5fd094a33c..56f7400140 100644
--- a/target/m68k/fpu_helper.c
+++ b/target/m68k/fpu_helper.c
@@ -538,17 +538,25 @@ void HELPER(fmod)(CPUM68KState *env, FPReg *res, FPReg 
*val0, FPReg *val1)
 
 void HELPER(frem)(CPUM68KState *env, FPReg *res, FPReg *val0, FPReg *val1)
 {
+    float_status fp_status;
+    FPReg fp_quot;
     uint32_t quotient;
     int sign;
 
+    /* Calculate quotient directly using round to nearest mode */
+    set_float_rounding_mode(float_round_nearest_even, &fp_status);
+    set_floatx80_rounding_precision(
+        get_floatx80_rounding_precision(&env->fp_status), &fp_status);
+    fp_quot.d = floatx80_div(val1->d, val0->d, &fp_status);
+
     res->d = floatx80_rem(val1->d, val0->d, &env->fp_status);
 
-    if (floatx80_is_any_nan(res->d)) {
+    if (floatx80_is_any_nan(fp_quot.d)) {
         return;
     }
 
-    sign = extractFloatx80Sign(res->d);
-    quotient = floatx80_to_int32(floatx80_abs(res->d), &env->fp_status);
+    sign = extractFloatx80Sign(fp_quot.d);
+    quotient = floatx80_to_int32(floatx80_abs(fp_quot.d), &env->fp_status);
     make_quotient(env, sign, quotient);
 }
 
-- 
2.30.2