Correct relative jumps range and adjust it for single core without delay-slot.

Setting bits 16 to 31 to 1 is incorrect, offset is shift
by two so bit 16 can be zero for jumps in range -64k to -128k.

Adjust relative offsets to compute target address same, as if there
is delay slot, for CPU variant without delay slot.
This allows to use same/standard MIPS assembler for mode
without delay slots.

Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>

2 files changed, 10 insertions, 6 deletions

diff --git a/qtmips_machine/core.cpp b/qtmips_machine/core.cpp
index 980a736..f290659 100644
--- a/qtmips_machine/core.cpp
+++ b/qtmips_machine/core.cpp
@@ -462,7 +462,7 @@ void Core::writeback(const struct dtMemory &dt) {
         regs->write_gp(dt.rwrite, dt.towrite_val);
 }
 
-bool Core::handle_pc(const struct dtDecode &dt) {
+bool Core::handle_pc(const struct dtDecode &dt, int32_t rel_adj) {
     bool branch = false;
     emit instruction_program_counter(dt.inst, dt.inst_addr, EXCAUSE_NONE);
 
@@ -497,10 +497,14 @@ bool Core::handle_pc(const struct dtDecode &dt) {
     emit fetch_jump_reg_value(false);
     emit fetch_branch_value(branch);
 
-    if (branch)
-        regs->pc_jmp((std::int32_t)(((dt.inst.immediate() & 0x8000) ? 0xFFFF0000 : 0) | (dt.inst.immediate() << 2)));
-    else
+    if (branch) {
+        std::int32_t rel_offset = dt.inst.immediate() << 2;
+        if (rel_offset & (1 << 17))
+            rel_offset -= 1 << 18;
+        regs->pc_jmp(rel_offset + rel_adj);
+    } else {
         regs->pc_inc();
+    }
     return branch;
 }
 
@@ -596,7 +600,7 @@ void CoreSingle::do_step(bool skip_break) {
         jump_branch_pc = jmp_delay_decode->inst_addr;
         *jmp_delay_decode = d; // Copy current decode
     } else {
-        handle_pc(d);
+        handle_pc(d, 4);
         jump_branch_pc = d.inst_addr;
     }
 
diff --git a/qtmips_machine/core.h b/qtmips_machine/core.h
index f70a19d..1c44550 100644
--- a/qtmips_machine/core.h
+++ b/qtmips_machine/core.h
@@ -245,7 +245,7 @@ protected:
     struct dtExecute execute(const struct dtDecode&);
     struct dtMemory memory(const struct dtExecute&);
     void writeback(const struct dtMemory&);
-    bool handle_pc(const struct dtDecode&);
+    bool handle_pc(const struct dtDecode&, std::int32_t rel_adj = 0);
 
     enum ExceptionCause memory_special(enum AccessControl memctl,
                            int mode, bool memread, bool memwrite,