Added some very untested csa and csb implementations, based on the PowerPC

ones.

mach/mips/libem/csa.s

@@ -0,0 +1,41 @@
+#
+.sect .text; .sect .rom; .sect .data; .sect .bss
+
+/* This is not a subroutine, but just a
+ * piece of code that computes the jump-
+ * address and jumps to it.
+ * traps if resulting address is zero
+ *
+ * Stack: ( value tableaddr -- )
+ */
+
+.define .csa
+.csa:
+	lw r4, 0(sp)            /* r4 = table */
+	lw r5, 0(sp)            /* r5 = value */
+	addiu sp, sp, 8
+
+	lw r6, 0(r4)            /* r6 = default target */
+	lw r7, 4(r4)            /* r7 = lower bound */
+	subu r5, r5, r6         /* adjust value */
+	bltz r5, 1f             /* jump to default if out of range */
+	nop
+
+	lw r7, 8(r4)            /* fetch range */
+	subu r7, r5, r7         /* compute (adjusted value - range) */
+	blez r7, 1f             /* jump to default if out of range */
+	nop
+
+	addiu r4, r4, 12        /* skip header */
+	sll r5, r5, 2           /* value = value<<2 */
+	addu r4, r4, r5         /* find address of target */
+	lw r6, 0(r4)            /* r6 = new target */
+
+1:
+	beq r6, zero, 2f        /* trap if null */
+	nop
+	jr r6                   /* otherwise jump */
+	nop
+2:
+	j .trap_ecase
+	nop

mach/mips/libem/csb.s

@@ -0,0 +1,47 @@
+#
+.sect .text; .sect .rom; .sect .data; .sect .bss
+
+/* this is not a subroutine, but just a
+ * piece of code that computes the jump-
+ * address and jumps to it.
+ * traps if resulting address is zero
+ *
+ * Stack: ( value tableaddr -- )
+ */
+
+.sect .text
+.define .csb
+.csb:
+	lw r4, 0(sp)             ! r4 = address of table
+	lw r5, 0(sp)             ! r5 = value
+	addiu sp, sp, 8
+
+	lw r6, 0(r4)             ! r6 = default target
+	lw r7, 4(r4)             ! r7 = table count
+
+2:
+	addiu r7, r7, -1         ! decrement count
+	bltz r7, 1f              ! exit loop if out
+	nop
+
+	lw r8, 8(r4)             ! candidate value
+	beq r8, r5, 3f           ! branch if equal
+	nop
+
+	addiu r4, r4, 8          ! next entry
+	b 2b
+	nop
+
+3:
+	/* We found an item in the table. */
+	lw r6, 12(r4)            ! load jump target
+	/* fall through */
+1:
+	beq r6, zero, 4f        /* trap if null */
+	nop
+	jr r6                   /* otherwise jump */
+	nop
+4:
+	j .trap_ecase
+	nop
+

mach/mips/libem/trp.s

@@ -8,6 +8,7 @@
 	li	r3, 20			! ECASE = 20 in h/em_abs.h
 	! FALLTHROUGH to .trp
 
+.define .trp
 .trp:
 	syscall 0