Don't have much to add except to note that early FORTRANs had a version of IF that took three statement numbers and did a (gasp) GOTO to the first if the expression in the IF was negative, to the second if it was 0, and to the third if it was positive.   And some mainframes had an instruction that did exactly that as well... Steve ----- Original Message ----- From: "Doug McIlroy" &lt;doug(a)cs.dartmouth.edu&gt; To:<tuhs@minnie.tuhs.org> Cc: Sent:Sat, 12 Aug 2017 21:58:19 -0400 Subject:[TUHS] origin of string.h and ctype.h Jon Steinhart &lt;jon(a)fourwinds.com&gt; asked this question (not on tuhs). It highlights some less well known contributors to research Unix. in or B The -1,0,1 return from comparisons stems from the interface of qsort, which was written by Lee McMahon. As far as I know, the interface for the comparison-function parameter originated with him, but conceivably he borrowed it from some other sort utility. The negative-zero-positive convention for the return value encouraged (and perhaps was motivated by) this trivial comparison function for integers int compar(a,b) { return(a-b); } This screws up on overflow, so cautious folks would write it with comparisons. And -1,0,1 were the easiest conventional values to return: int compar(a,b) { if(a<b) return(-1); if(a>b) return(1); return(0); } qsort was in v2. In v3 a string-comparison routine called "compar" appeared, with a man page titled "string comparison for sort". So the convention was established early on. Compar provided the model for strcmp, one of a package of basic string operations that came much later, in v7, under the banner of string.h and ctype.h. These packages were introduced at the urging of Nils-Peter Nelson, a good friend of the Unix lab, who was in the Bell Labs comp center. Here's the story in his own words. I wrote a memo to dmr with some suggestions for additions to C. I asked for the str... because the mainframes had single instructions to implement them. I know for sure I had a blindingly fast implementation of isupper, ispunct, etc. I had a table of length 128 integers for the ascii character set; I assigned bits for upper, lower, numeric, punct, control, etc. So ispunct(c) became #define PUNCT 0400 return(qtable[c]&PUNCT) instead of if(c==':' || c ==';' || ... [or switch(c) { default: return 0; case ':': case ';': ... return 1; } MDM] dmr argued people could easily write their own but when I showed him my qtable was 20 times faster he gave in. I also asked for type logical which dmr implemented as unsigned, which was especially useful when bitfields were implemented (a 2 bit int would have values -2, -1, 0, 1 instead of 0, 1, 2, 3). I requested a way to interject assembler, which became asm() (yes, a bad idea).