[TUHS] arithmetic IF (was origin of string.h and ctype.h)

[Doug McIlroy]

> [Fortran's optimization]  worked so well that the results that came out of the compiler
> sometimes suprised the compiler writers!

Except when it didn't. They gave particular attention to nested
loops with subscripted variables, exemplified by linear-algebra
computations. But their algorithms behaved quite wildly on
nonstandard loops. Vic Vyssotsky cooked up a nest of loops
surrounding a single awful statement that filled up the
maximum 10 continuation lines with triple subscripts in all
permutations of several variables. That statement compiled
into thousands of instructions, far more than a naively
written compiler would have produced.

doug