From 33f748f77867bc8efd3783cfc141ed8406c48256 Mon Sep 17 00:00:00 2001
From: Jim Wilcoxson <prirun@gmail.com>
Date: Mon, 20 Apr 2020 16:14:03 +0000
Subject: [PATCH] em.c: simpler iget16 and iget16t with same performance
 Previously iget16 was used for all instruction fetches, with the assumption
 that any could trap.  But actually, only the first word of the instruction
 stream can trap in V mode, which is why these instructions must be short. 
 Both words of a long R-mode instruction can trap.

Tested change by booting R19 with and without -DFAST, all other revs
with -DFAST, and basic with trace on in R19 (this executes code from
the DFAC)
---
 em.c | 32 ++++++++------------------------
 1 file changed, 8 insertions(+), 24 deletions(-)

diff --git a/em.c b/em.c
index 8278bfc..c40494a 100644
--- a/em.c
+++ b/em.c
@@ -1300,32 +1300,16 @@ static long long get64r(ea_t ea, ea_t rpring) {
    page instead of on every 16-bit fetch from the instruction stream.
 */
 
-#ifdef FAST
-
-unsigned short iget16t(ea_t ea) {
-  unsigned short access;
-
-  if (*(int *)&ea >= 0) {
-    gv.brp[RPBR].memp = MEM + (mapva(ea, RP, RACC, &access) & 0xFFFFFC00);
-    gv.brp[RPBR].vpn = ea & 0x0FFFFC00;
-    return swap16(gv.brp[RPBR].memp[ea & 0x3FF]);
-  }
-  return get16trap(ea);
+static inline unsigned short iget16t(ea_t ea) {
+  eap = &gv.brp[RPBR];
+  return get16t(ea);
 }
 
 static inline unsigned short iget16(ea_t ea) {
-
-  if ((ea & 0x8FFFFC00) == (gv.brp[RPBR].vpn & 0x0FFFFFFF))
-    return swap16(gv.brp[RPBR].memp[ea & 0x3FF]);
-  else
-    return iget16t(ea);
+  eap = &gv.brp[RPBR];
+  return get16(ea);
 }
 
-#else
-#define iget16(ea) get16t((ea))
-#define iget16t(ea) get16t((ea))
-#endif
-
 static inline void put16(unsigned short value, ea_t ea) {
   unsigned short access;
 
@@ -2255,7 +2239,7 @@ special:
 #endif
 
   if (class < 2) {                               /* class 0/1 */
-    ea = iget16(RP);                             /* get A from next word */
+    ea = iget16t(RP);                            /* get A from next word */
     INCRP;
     TRACE(T_EAR, " Class %d, new ea=%o\n", class, ea);
     if (class == 1)
@@ -2284,7 +2268,7 @@ special:
 
   } else if (i && x) {                           /* class 2/3, ix=11 */
     TRACE(T_EAR, " class 2/3, ix=11\n");
-    ea = iget16(RP);                             /* get A from next word */
+    ea = iget16t(RP);                            /* get A from next word */
     INCRP;
     TRACE(T_EAR, " ea=%o\n", ea);
     if (class == 3) {
@@ -5187,7 +5171,7 @@ fetch:
 
   inst = iget16(RP | ((RPL >= gv.livereglim || (getcrs16(KEYS) & 0016000) == 010000) ? 0 : 0x80000000));
 #else
-  inst = iget16(RP);
+  inst = iget16t(RP);
 #endif
 
   INCRP;