x86 use the least significant n bits, except the original 8086 and 8088 when the shift count is in the CL register, in which case all 8 bits would be used (this was how the 80186 was distinguished from the 8086). The use of just n bits is common enough among modern archs, but 32-bit ARM (e.g. in ARM Cortex M0+ or M4 microcontrollers) is an exception, since it uses the low eight bits of the operand (but still ignores the higher bits). Enforcing a result of zero when the count is higher than th...
