[PATCH 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
---
 target/m68k/fpu_helper.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/target/m68k/fpu_helper.c b/target/m68k/fpu_helper.c
index 18594a35af..ce6f2cd2b9 100644
--- a/target/m68k/fpu_helper.c
+++ b/target/m68k/fpu_helper.c
@@ -538,14 +538,23 @@ void HELPER(fmod)(CPUM68KState *env, FPReg *res, FPReg 
*val0, FPReg *val1)
 
 void HELPER(frem)(CPUM68KState *env, FPReg *res, FPReg *val0, FPReg *val1)
 {
+    FPReg fp_quot;
+    float_status fp_status;
+
+    /* 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;
     }
 
-    make_quotient(env, extractFloatx80Sign(res->d),
-                  floatx80_to_int32(res->d, &env->fp_status));
+    make_quotient(env, extractFloatx80Sign(fp_quot.d),
+                  abs(floatx80_to_int32(fp_quot.d, &env->fp_status)));
 }
 
 void HELPER(fgetexp)(CPUM68KState *env, FPReg *res, FPReg *val)
-- 
2.30.2