DC(1) DC(1) NAME dc - desk calculator SYNOPSIS dc [ file ] DESCRIPTION Dc is an arbitrary precision desk calculator. Ordinarily it operates on decimal integers, but one may specify an input base, output base, and a number of fractional digits to be maintained. The overall structure of dc is a stacking (reverse Polish) calculator. If an argument is given, input is taken from that file until its end, then from the stan- dard input. The following constructions are recognized: number The value of the number is pushed on the stack. A num- ber is an unbroken string of the digits 0-9A-F or 0-9a-f. A hexadecimal number beginning with a lower case letter must be preceded by a zero to distinguish it from the command associated with the letter. It may be preceded by an underscore _ to input a negative num- ber. Numbers may contain decimal points. + - / * % ^ Add `+', subtract `-', multiply `*', divide `/', remainder `%', or exponentiate `^' the top two values on the stack. The two entries are popped off the stack; the result is pushed on the stack in their place. Any fractional part of an exponent is ignored. sx Sx Pop the top of the stack and store into a register named x, where x may be any character. Under operation S register x is treated as a stack and the value is pushed on it. lx Lx Push the value in register x onto the stack. The reg- ister x is not altered. All registers start with zero value. Under operation L register x is treated as a stack and its top value is popped onto the main stack. d Duplicate the top value on the stack. p Print the top value on the stack. The top value remains unchanged. P interprets the top of the stack as a text string, removes it, and prints it. f Print the values on the stack. Page 1 Plan 9 (printed 4/22/21) DC(1) DC(1) q Q Exit the program. If executing a string, the recursion level is popped by two. Under operation Q the top value on the stack is popped and the string execution level is popped by that value. x Treat the top element of the stack as a character string and execute it as a string of dc commands. X Replace the number on the top of the stack with its scale factor. [ ... ] Put the bracketed text string on the top of the stack. <x >x =x Pop and compare the top two elements of the stack. Register x is executed if they obey the stated rela- tion. v Replace the top element on the stack by its square root. Any existing fractional part of the argument is taken into account, but otherwise the scale factor is ignored. ! Interpret the rest of the line as a shell command. c Clear the stack. i The top value on the stack is popped and used as the number base for further input. I Push the input base on the top of the stack. o The top value on the stack is popped and used as the number base for further output. In bases larger than 10, each `digit' prints as a group of decimal digits. O Push the output base on the top of the stack. k Pop the top of the stack, and use that value as a non- negative scale factor: the appropriate number of places are printed on output, and maintained during multipli- cation, division, and exponentiation. The interaction of scale factor, input base, and output base will be reasonable if all are changed together. z Push the stack level onto the stack. Z Replace the number on the top of the stack with its length. Page 2 Plan 9 (printed 4/22/21) DC(1) DC(1) ? A line of input is taken from the input source (usually the terminal) and executed. ; : Used by bc for array operations. The scale factor set by k determines how many digits are kept to the right of the decimal point. If s is the current scale factor, sa is the scale of the first operand, sb is the scale of the second, and b is the (integer) second operand, results are truncated to the following scales. +,- max(sa,sb) * min(sa+sb , max(s,sa,sb)) / s % so that dividend = divisor*quotient + remainder; remainder has sign of dividend ^ min(sax|b|, max(s,sa)) v max(s,sa) EXAMPLES Print the first ten values of n! [la1+dsa*pla10>y]sy 0sa1 lyx Print π. 1sq180sr60st2si[3li*1+d1+*3*suli27*12-lq*5lr*+lt 5*/d48+Psy10lqlid2*1-***10lulqli5*2-*lr+lylt*-** srsqlult*stli1+silmx]smlmx SOURCE /sys/src/cmd/dc.c SEE ALSO bc(1), hoc(1) DIAGNOSTICS x `is unimplemented', where x is an octal number: an inter- nal error. `Out of headers' for too many numbers being kept around. `Nesting depth' for too many levels of nested execution. BUGS When the input base exceeds 16, there is no notation for digits greater than F. Past its time. Page 3 Plan 9 (printed 4/22/21)