为什么STM32对CRC不支持even polynomials

树欲静

看STM32的手册0X1，看到了
Polynomial programmability (STM32F07x and STM32F09x devices only)
The polynomial coefficients are fully programmable through the CRC_POL register, and the
polynomial size can be configured to be 7, 8, 16 or 32 bits by programming the
POLYSIZE[1:0] bits in the CRC_CR register. Even polynomials are not supported
我的理解是配置的多项式只能由奇数个1，是这么理解的么？为什么会有这个要求？求指导