Use data_minus_addr to get a tiny tiny speedup

so tiny, I can't measure it. but I can look at the disassembly and see one less instruction
kenardi · Jun 22, 2017 · c24ad25 · c24ad25
1 parent c3d0189
commit c24ad25
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Showing 3 changed files with 10 additions and 8 deletions.
diff --git a/emu/memory.c b/emu/memory.c
@@ -151,9 +151,9 @@ void *tlb_handle_miss(struct mem *mem, addr_t addr, int type) {
     else
         // 1 is not a valid page so this won't look like a hit
         tlb->page_if_writable = TLB_PAGE_EMPTY;
-    tlb->data = pt->data;
-    mem->dirty_page = PAGE(addr);
-    return (char *) tlb->data + OFFSET(addr);
+    tlb->data_minus_addr = (uintptr_t) pt->data - TLB_PAGE(addr);
+    mem->dirty_page = TLB_PAGE(addr);
+    return (void *) (tlb->data_minus_addr + addr);
 }
 
 __attribute__((constructor))

diff --git a/emu/memory.h b/emu/memory.h
@@ -62,11 +62,11 @@ void pt_dump(struct mem *mem);
 struct tlb_entry {
     page_t page;
     page_t page_if_writable;
-    void *data;
+    uintptr_t data_minus_addr;
 };
 #define TLB_BITS 10
 #define TLB_SIZE (1 << TLB_BITS)
-#define TLB_INDEX(addr) (((addr) & 0x003ff000) >> 12)
+#define TLB_INDEX(addr) ((addr >> PAGE_BITS) & (TLB_SIZE - 1))
 #define TLB_READ 0
 #define TLB_WRITE 1
 #define TLB_PAGE(addr) (addr & 0xfffff000)
@@ -76,7 +76,7 @@ void *tlb_handle_miss(struct mem *mem, addr_t addr, int type);
 forceinline void *mem_read_ptr(struct mem *mem, addr_t addr) {
     struct tlb_entry entry = mem->tlb[TLB_INDEX(addr)];
     if (entry.page == TLB_PAGE(addr)) {
-        void *address = (char *) entry.data + OFFSET(addr);
+        void *address = (void *) (entry.data_minus_addr + addr);
         postulate(address != NULL);
         return address;
     }
@@ -86,8 +86,8 @@ forceinline void *mem_read_ptr(struct mem *mem, addr_t addr) {
 forceinline void *mem_write_ptr(struct mem *mem, addr_t addr) {
     struct tlb_entry entry = mem->tlb[TLB_INDEX(addr)];
     if (entry.page_if_writable == TLB_PAGE(addr)) {
-        mem->dirty_page = PAGE(addr);
-        void *address = (char *) entry.data + OFFSET(addr);
+        mem->dirty_page = TLB_PAGE(addr);
+        void *address = (void *) (entry.data_minus_addr + addr);
         postulate(address != NULL);
         return address;
     }

diff --git a/emu/modrm.h b/emu/modrm.h
@@ -8,6 +8,7 @@ struct regptr {
     reg_id_t reg32_id;
     reg_id_t reg64_id;
 };
+#if DEBUG_LOG
 static const char *regptr_name(struct regptr regptr) {
     static char buf[15];
     sprintf(buf, "%s/%s/%s",
@@ -16,6 +17,7 @@ static const char *regptr_name(struct regptr regptr) {
             reg32_name(regptr.reg32_id));
     return buf;
 }
+#endif
 
 struct modrm_info {
     // MOD/RM BITS