diff --git a/mach/mips/libem/com.s b/mach/mips/libem/com.s
index fae0d64e5..ffabe9f5e 100644
--- a/mach/mips/libem/com.s
+++ b/mach/mips/libem/com.s
@@ -21,6 +21,7 @@
 	addiu r5, r5, 4
 	addiu r4, r4, -1
 	bne r4, zero, 1b
+	nop
 
 	jr ra
 	nop
diff --git a/mach/mips/libem/xor.s b/mach/mips/libem/xor.s
new file mode 100644
index 000000000..ad23b1d52
--- /dev/null
+++ b/mach/mips/libem/xor.s
@@ -0,0 +1,30 @@
+#
+.sect .text; .sect .rom; .sect .data; .sect .bss
+
+/*
+ * Set xor..
+ * Stack: ( a b size -- a^b )
+ */
+
+.sect .text
+.define .xor
+.xor:
+	lw r4, 0(sp)        ! r4 = size
+	addiu sp, sp, 4     ! sp points at b
+	addu r5, sp, r4     ! r5 points at a
+	srl r4, r4, 2       ! r4 = count of words
+
+1:
+	lw at, 0(r5)        ! load a
+	lw r6, 0(sp)        ! load b
+	xor at, at, r6      ! combine
+	sw at, 0(r5)        ! write back to a
+	addiu r5, r5, 4
+	addiu sp, sp, 4
+	addiu r4, r4, -1
+	bne r4, zero, 1b
+	nop
+
+	jr ra
+	nop
+
diff --git a/mach/mips/libem/zer.s b/mach/mips/libem/zer.s
index 6941d340b..b48fb8ffc 100644
--- a/mach/mips/libem/zer.s
+++ b/mach/mips/libem/zer.s
@@ -18,6 +18,7 @@
 	sw zero, 0(sp)
 	addiu r4, r4, -1
 	bne r4, zero, 1b
+	nop
 
 	jr ra
 	nop
diff --git a/tests/plat/core/and_e.e b/tests/plat/core/and_e.e
new file mode 100644
index 000000000..1bdf3d5ed
--- /dev/null
+++ b/tests/plat/core/and_e.e
@@ -0,0 +1,54 @@
+#
+    mes 2, EM_WSIZE, EM_PSIZE
+
+    exp $_m_a_i_n
+    pro $_m_a_i_n, 0
+
+	/* And word-sized set */
+
+four
+	rom EM_WSIZE
+
+	loc 32769
+	loc 1
+	loe four		/* to defeat constant folding */
+	and
+	loc 1
+	cmu EM_WSIZE
+	zeq *1
+
+    loc __LINE__
+    cal $fail
+    asp 4
+1
+
+	/* And triple-word-sized set */
+
+four_by_three
+	rom EM_WSIZE*3
+
+	loc 32769
+	loc 32770
+	loc 32772
+	loc 1
+	loc 2
+	loc 4
+	loe four_by_three
+	and
+	loc 4
+	cmu EM_WSIZE
+	zne *2
+	loc 2
+	cmu EM_WSIZE
+	zne *2
+	loc 1
+	cmu EM_WSIZE
+	zeq *3
+2
+	loc __LINE__
+	cal $fail
+	asp 4
+3
+
+    cal $finished
+    end
diff --git a/tests/plat/core/ior_e.e b/tests/plat/core/ior_e.e
new file mode 100644
index 000000000..9f4a0d985
--- /dev/null
+++ b/tests/plat/core/ior_e.e
@@ -0,0 +1,54 @@
+#
+    mes 2, EM_WSIZE, EM_PSIZE
+
+    exp $_m_a_i_n
+    pro $_m_a_i_n, 0
+
+	/* Or word-sized set */
+
+four
+	rom EM_WSIZE
+
+	loc 0
+	loc 1
+	loe four		/* to defeat constant folding */
+	ior
+	loc 1
+	cmu EM_WSIZE
+	zeq *1
+
+    loc __LINE__
+    cal $fail
+    asp 4
+1
+
+	/* Or triple-word-sized set */
+
+four_by_three
+	rom EM_WSIZE*3
+
+	loc 16
+	loc 32
+	loc 64
+	loc 1
+	loc 2
+	loc 3
+	loe four_by_three
+	ior
+	loc 67
+	cmu EM_WSIZE
+	zne *2
+	loc 34
+	cmu EM_WSIZE
+	zne *2
+	loc 17
+	cmu EM_WSIZE
+	zeq *3
+2
+	loc __LINE__
+	cal $fail
+	asp 4
+3
+
+    cal $finished
+    end
diff --git a/tests/plat/core/xor_e.e b/tests/plat/core/xor_e.e
new file mode 100644
index 000000000..8218ee63c
--- /dev/null
+++ b/tests/plat/core/xor_e.e
@@ -0,0 +1,54 @@
+#
+    mes 2, EM_WSIZE, EM_PSIZE
+
+    exp $_m_a_i_n
+    pro $_m_a_i_n, 0
+
+	/* Xor word-sized set */
+
+four
+	rom EM_WSIZE
+
+	loc 32769
+	loc 1
+	loe four		/* to defeat constant folding */
+	xor
+	loc 32768
+	cmu EM_WSIZE
+	zeq *1
+
+    loc __LINE__
+    cal $fail
+    asp 4
+1
+
+	/* Xor triple-word-sized set */
+
+four_by_three
+	rom EM_WSIZE*3
+
+	loc 32769
+	loc 32770
+	loc 32772
+	loc 1
+	loc 2
+	loc 4
+	loe four_by_three
+	xor
+	loc 32768
+	cmu EM_WSIZE
+	zne *2
+	loc 32768
+	cmu EM_WSIZE
+	zne *2
+	loc 32768
+	cmu EM_WSIZE
+	zeq *3
+2
+	loc __LINE__
+	cal $fail
+	asp 4
+3
+
+    cal $finished
+    end