From: Toni Wilen <twilen@winuae.net>
Date: Mon, 4 Dec 2017 13:52:21 +0000 (+0200)
Subject: Accurate DIV overflow undocumented flags.
X-Git-Tag: 3600~51
X-Git-Url: https://git.unchartedbackwaters.co.uk/w/?a=commitdiff_plain;h=1093f40e2e913c700f7ab4fc6c2dbe16470760e2;p=francis%2Fwinuae.git

Accurate DIV overflow undocumented flags.
---

diff --git a/gencpu.cpp b/gencpu.cpp
index 4d869e21..5b267362 100644
--- a/gencpu.cpp
+++ b/gencpu.cpp
@@ -4371,13 +4371,7 @@ bccl_not68020:
 		/* The N flag appears to be set each time there is an overflow.
 		 * Weird. but 68020 only sets N when dst is negative.. */
 		printf ("\t\tif (newv > 0xffff) {\n");
-		printf ("\t\t\tSET_VFLG (1);\n");
-#ifdef UNDEF68020
-		if (cpu_level >= 2)
-			printf ("\t\t\tif (currprefs.cpu_level == 0 || dst < 0) SET_NFLG (&regs, 1);\n");
-		else /* ??? some 68000 revisions may not set NFLG when overflow happens.. */
-#endif
-			printf ("\t\t\tSET_NFLG (1);\n");
+		printf ("\t\t\tsetdivuoverflowflags((uae_u32)dst, (uae_u16)src);\n");
 		printf ("\t\t} else {\n");
 		printf ("\t\t"); genflags (flag_logical, sz_word, "newv", "", "");
 		printf ("\t\t\tnewv = (newv & 0xffff) | ((uae_u32)rem << 16);\n");
@@ -4412,19 +4406,12 @@ bccl_not68020:
 		addcycles000_nonces("\t\t", "(getDivs68kCycles((uae_s32)dst, (uae_s16)src)) - 4");
 		fill_prefetch_next ();
 		printf ("\tif (dst == 0x80000000 && src == -1) {\n");
-		printf ("\t\tSET_VFLG (1);\n");
-		printf ("\t\tSET_NFLG (1);\n");
+		printf ("\t\tsetdivsoverflowflags((uae_s32)dst, (uae_s16)src);\n");
 		printf ("\t} else {\n");
 		printf ("\t\tuae_s32 newv = (uae_s32)dst / (uae_s32)(uae_s16)src;\n");
 		printf ("\t\tuae_u16 rem = (uae_s32)dst %% (uae_s32)(uae_s16)src;\n");
 		printf ("\t\tif ((newv & 0xffff8000) != 0 && (newv & 0xffff8000) != 0xffff8000) {\n");
-		printf ("\t\t\tSET_VFLG (1);\n");
-#ifdef UNDEF68020
-		if (cpu_level > 0)
-			printf ("\t\t\tif (currprefs.cpu_level == 0) SET_NFLG (&regs, 1);\n");
-		else
-#endif
-			printf ("\t\t\tSET_NFLG (1);\n");
+		printf ("\t\t\tsetdivsoverflowflags((uae_s32)dst, (uae_s16)src);\n");
 		printf ("\t\t} else {\n");
 		printf ("\t\t\tif (((uae_s16)rem < 0) != ((uae_s32)dst < 0)) rem = -rem;\n");
 		genflags (flag_logical, sz_word, "newv", "", "");
diff --git a/include/newcpu.h b/include/newcpu.h
index e3790155..700e3d9c 100644
--- a/include/newcpu.h
+++ b/include/newcpu.h
@@ -633,7 +633,9 @@ extern void m68k_dumpstate (uaecptr, uaecptr *);
 extern void m68k_dumpcache (bool);
 extern int getDivu68kCycles (uae_u32 dividend, uae_u16 divisor);
 extern int getDivs68kCycles (uae_s32 dividend, uae_s16 divisor);
-extern void divbyzero_special (bool issigned, uae_s32 dst);
+extern void divbyzero_special(bool issigned, uae_s32 dst);
+extern void setdivuoverflowflags(uae_u32 dividend, uae_u16 divisor);
+extern void setdivsoverflowflags(uae_s32 dividend, uae_u16 divisor);
 extern void protect_roms (bool);
 extern void unprotect_maprom (void);
 extern bool is_hardreset(void);
diff --git a/newcpu_common.cpp b/newcpu_common.cpp
index 1f82073e..919c98dd 100644
--- a/newcpu_common.cpp
+++ b/newcpu_common.cpp
@@ -771,6 +771,64 @@ void divbyzero_special (bool issigned, uae_s32 dst)
 	}
 }
 
+/* DIVU overflow
+ *
+ * 68000: V=1 N=1
+ * 68020: V=1 N=X
+ * 68040: V=1
+ * 68060: V=1
+ *
+ * X) N is set if original 32-bit destination value is negative.
+ *
+ */
+
+void setdivuoverflowflags(uae_u32 dividend, uae_u16 divisor)
+{
+	if (currprefs.cpu_model >= 68040) {
+		SET_VFLG(1);
+	} else if (currprefs.cpu_model >= 68020) {
+		SET_VFLG(1);
+		if ((uae_s32)dividend < 0)
+			SET_NFLG(1);
+	} else {
+		SET_VFLG(1);
+		SET_NFLG(1);
+	}
+}
+
+/*
+ * DIVS overflow
+ *
+ * 68000: V = 1 N = 1
+ * 68020: V = 1 ZN = X
+ * 68040: V = 1
+ * 68060: V = 1
+ *
+ * X) if absolute overflow(Check getDivs68kCycles for details) : Z = 0, N = 0
+ * if not absolute overflow : N is set if internal result BYTE is negative, Z is set if it is zero!
+ *
+ */
+
+void setdivsoverflowflags(uae_s32 dividend, uae_u16 divisor)
+{
+	if (currprefs.cpu_model >= 68040) {
+		SET_VFLG(1);
+	} else if (currprefs.cpu_model >= 68020) {
+		SET_VFLG(1);
+		// absolute overflow?
+		if (((uae_u32)abs(dividend) >> 16) >= (uae_u16)abs(divisor))
+			return;
+		uae_u32 aquot = (uae_u32)abs(dividend) / (uae_u16)abs(divisor);
+		if ((uae_s8)aquot == 0)
+			SET_ZFLG(1);
+		if ((uae_s8)aquot < 0)
+			SET_NFLG(1);
+	} else {
+		SET_VFLG(1);
+		SET_NFLG(1);
+	}
+}
+
 #ifndef CPUEMU_68000_ONLY
 
 #if !defined (uae_s64)