hexChars: dw 0, 0x03ff0000, 0x0000007e, 0x0000007e, 0, 0, 0, 0

# hexChars[ch >> 5] & (1 << (ch & 0x1F))

srl t0, a0, 5		# ch >> 5
lw t0, hexChars(t0)	#
andi t1, a0, 0x1F	# ch & 0x1F
addi t2, zero, 1	# 1
sll t2, a0, t1		# 1 << (ch & 0x1F)
and t0, t0, t2		# t0 is 0 if not a hex char