Floyd and Knuth investigated in 1990 register machines which can add, subtract and compare integers as primitive operations. They asked whether their current bound on the number of registers for multiplying and dividing fast (running in time linear in the size of the input) can be improved and whether one can output fast the powers of two summing up to a positive integer in subquadratic time. Both questions are answered positively. Furthermore, it is shown that every function computed by only one register is automatic and that automatic functions with one input can be computed with four registers in linear time; automatic functions with a larger number of inputs can be computed with 5 registers in linear time. There is a nonautomatic function with one input which can be computed with two registers in linear time.

翻译：1990年调查的Floyd 和 Knuth 注册机器可以将整数作为原始操作进行添加、减法和比较。 他们询问,它们目前对快速增减和除法的登记册数量的约束(输入大小的时线性运行)是否可以改进,以及是否可以在亚赤道时间快速输出两个总和的功率,在正整数中得出正整数。这两个问题都得到肯定回答。此外,还显示,仅用一个登记册计算的每个函数都是自动的,一个输入的自动函数可以用四个登记册以线性时间计算;输入量较大的自动函数可以用5个登记册以线性时间计算。有一个非自动函数,一个输入可以用两个登记册以线性时间计算。