fpu, config: introduce $_ignore_fpe

To be able to run ipp540s, we can completely ignore floating point
exceptions, by masking CWD and returning, so IRQ13 is never triggered.

Fixes dosemu2#2724

Author: bartoldeman

etc/dosemu.conf

@@ -77,6 +77,11 @@
 
 # $_mathco = (on)
 
+# ignore floating point exceptions, (off) or (on), default = (off)
+# this helps for e.g. ipp540s which FPEs on CPUs that are fast enough
+
+# $_ignore_fpe = (off)
+
 # 0 = all CPU power to DOSEMU; default = 1 = nicest, then higher:more CPU power
 
 # $_hogthreshold = (1)

etc/global.conf

@@ -107,6 +107,7 @@ else
 
   timer 0
   mathco $_mathco
+  ignore_fpe $_ignore_fpe
   $xxx = "cpu ", $_cpu;
   $$xxx
   cpuemu $$_cpuemu

src/base/emu-i386/cpu.c

@@ -361,6 +361,15 @@ static void raise_fpu_irq(void)
 
 int fpu_fpe_handler (unsigned char *csp)
 {
+  if (config.ignore_fpe) {
+    if (_CPU_VM_CURRENT() == CPUVM_KVM)
+      kvm_get_fpu();
+    dbug_printf("coprocessor exception, ignoring by masking in CW because of $_ignore_fpe\n");
+    vm86_fpu_state.cwd |= 0x7f;
+    if (_CPU_VM_CURRENT() == CPUVM_KVM)
+      kvm_update_fpu();
+    return 0;
+  }
   if (fpu_ignne) {
     /* do some basic emulation:
        we only deal with control FPU instructions,

src/base/init/lexer.l

@@ -321,6 +321,7 @@ terminal		RETURN(TERMINAL);
 video			RETURN(VIDEO);
 emuretrace		RETURN(EMURETRACE);
 mathco			RETURN(MATHCO);
+ignore_fpe		RETURN(IGNORE_FPE);
 cpu			RETURN(CPU);
 cpuspeed		RETURN(CPUSPEED);
 bootdrive		RETURN(BOOTDRIVE);

src/base/init/parser.y

@@ -232,7 +232,7 @@ enum {
 %token FASTFLOPPY HOGTHRESH SPEAKER IPXSUPPORT IPXNETWORK NOVELLHACK
 %token ETHDEV TAPDEV VDESWITCH SLIRPARGS NETSOCK VNET
 %token DEBUG MOUSE SERIAL COM KEYBOARD TERMINAL VIDEO EMURETRACE TIMER
-%token MATHCO CPU CPUSPEED BOOTDRIVE SWAP_BOOTDRIVE
+%token MATHCO IGNORE_FPE CPU CPUSPEED BOOTDRIVE SWAP_BOOTDRIVE
 %token L_XMS L_DPMI DPMI_BASE PM_DOS_API NO_NULL_CHECKS
 %token PORTS DISK DOSMEM EXT_MEM
 %token L_EMS UMB_A0 UMB_B0 UMB_B8 UMB_F0 HMA DOS_UP
@@ -637,6 +637,7 @@ line:		CHARSET '{' charset_flags '}' {}
 		    if ($2 > 0) c_printf("CONF: %dk bytes XMS memory\n", $2);
 		    }
 		| MATHCO bool		{ config.mathco = ($2!=0); }
+		| IGNORE_FPE bool	{ config.ignore_fpe = ($2!=0); }
 		| IPXSUPPORT bool
 		    {
 		    config.ipxsup = ($2!=0);

src/include/emu.h

@@ -225,7 +225,7 @@ typedef struct config_info {
        boolean exitearly;
        boolean quiet;
        int     realcpu;
-       boolean mathco, smp, cpuprefetcht0, cpufxsr, cpusse, umip;
+       boolean mathco, ignore_fpe, smp, cpuprefetcht0, cpufxsr, cpusse, umip;
        boolean ipxsup;
        unsigned ipx_net;
        int     vnet;