DC(1) BSD Reference Manual DC(1)

dc- desk calculator

dc[-x] [-eexpression] [file]

dcis an arbitrary precision arithmetic package. The overall structure ofdcis a stacking (reverse Polish) calculator i.e. numbers are stored on a stack. Adding a number pushes it onto the stack. Arithmetic operations pop arguments off the stack and push the results. See also the bc(1) utility, which is a preprocessor fordcproviding infix notation and a C-like syntax which implements functions and reasonable control struc- tures for programs. The options are as follows:-eexpressionEvaluateexpression. If multiple-eoptions are specified, they will be processed in the order given.-xEnable extended register mode. This mode is used by bc(1) to al- low more than 256 registers. SeeRegistersfor a more detailed description. If neitherexpressionnorfileare specified on the command line,dcreads from the standard input. Otherwiseexpressionandfileare pro- cessed anddcexits. Ordinarily,dcoperates on decimal integers, but one may specify an input base, output base, and a number of fractional digits (scale) to be main- tained. Whitespace is ignored, except where it signals the end of a number, end of a line or when a register name is expected. The following constructions are recognized:numberThe value of the number is pushed on the stack. A number is an unbroken string of the digits 0-9 and letters A-F. It may be pre- ceded by an underscore ('_') to input a negative number. A number may contain a single decimal point. A number may also contain the characters A-F, with the values 10-15.+ - / * % ~ ^The top two values on the stack are added (+), subtracted (-), multiplied (*), divided (/), remaindered (%), divided and remain- dered (~), or exponentiated (^). 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. For addition and subtraction, the scale of the result is the max- imum of scales of the operands. For division the scale of the result is defined by the scale set by thekoperation. For multi- plication, the scale is defined by the expressionmin(a+b,max(a,b,scale)), whereaandbare the scales of the operands, andscaleis the scale defined by thekoperation. For exponentiation with a non-negative exponent, the scale of the result ismin(a*b,max(scale,a)), whereais the scale of the base, andbis thevalueof the exponent. If the exponent is negative, the scale of the result is the scale defined by thekoperation. In the case of the division and modulus operator (~), the resul- tant quotient is pushed first followed by the remainder. This is a shorthand for the sequence: x y / x y % The division and modulus operator is a non-portable extension.aPop the top value from the stack. If that value is a number, com- pute the integer part of the number modulo 256. If the result is zero, push an empty string. Otherwise push a one character string by interpreting the computed value as an ASCII character. If the top value is a string, push a string containing the first character of the original string. If the original string is emp- ty, an empty string is pushed back. Theaoperator is a non- portable extension.cAll values on the stack are popped.dThe top value on the stack is duplicated.fAll values on the stack are printed, separated by newlines.GThe top two numbers are popped from the stack and compared. A one is pushed if the top of the stack is equal to the second number on the stack. A zero is pushed otherwise. This is a non-portable extension.IPushes the input base on the top of the stack.iThe top value on the stack is popped and used as the base for further input. The initial input base is 10.JPop the top value from the stack. The recursion level is popped by that value and, following that, the input is skipped until the first occurrence of theMoperator. TheJoperator is a non- portable extension, used by the bc(1) command.KThe current scale factor is pushed onto the stack.kThe top of the stack is popped, and that value is used as a non- negative scale factor: the appropriate number of places are printed on output, and maintained during multiplication, divi- sion, and exponentiation. The interaction of scale factor, input base, and output base will be reasonable if all are changed to- gether.LxRegisterxis treated as a stack and its top value is popped onto the main stack.lxThe value in registerxis pushed on the stack. The registerxis not altered. Initially, all registers contain the value zero.MMark used by theJoperator. TheMoperator is a non-portable ex- tensions, used by the bc(1) command.NThe top of the stack is replaced by one if the top of the stack is equal to zero. If the top of the stack is unequal to zero, it is replaced by zero. This is a non-portable extension.nThe top value on the stack is popped and printed without a new- line. This is a non-portable extension.OPushes the output base on the top of the stack.oThe top value on the stack is popped and used as the base for further output. The initial output base is 10.PThe top of the stack is popped. If the top of the stack is a string, it is printed without a trailing newline. If the top of the stack is a number, it is interpreted as a base 256 number, and each digit of this base 256 number is printed as an ASCII character, without a trailing newline.pThe top value on the stack is printed with a trailing newline. The top value remains unchanged.QThe top value on the stack is popped and the string execution level is popped by that value.qExits the program. If executing a string, the recursion level is popped by two.RThe top of the stack is removed (popped). This is a non-portable extension.rThe top two values on the stack are reversed (swapped). This is a non-portable extension.SxRegisterxis treated as a stack. The top value of the main stack is popped and pushed on it.sxThe top of the stack is popped and stored into a register namedx.vReplaces the top element on the stack by its square root. The scale of the result is the maximum of the scale of the argument and the current value of scale.XReplaces the number on the top of the stack with its scale fac- tor. If the top of the stack is a string, replace it with the in- teger 0.xTreats the top element of the stack as a character string and ex- ecutes it as a string ofdccommands.ZReplaces the number on the top of the stack with its length. The length of a string is its number of characters. The length of a number is its number of digits, not counting the minus sign and decimal point.zThe stack level is pushed onto the stack.[...]Puts the bracketed ASCII string onto the top of the stack. If the string includes brackets, these must be properly balanced. The backslash character ('\') may be used as an escape character, making it possible to include unbalanced brackets in strings. To include a backslash in a string, use a double backslash.<x>x=x!<x!>x!=xThe top two elements of the stack are popped and compared. Regis- terxis executed if they obey the stated relation.<xey>xey=xey!<xey!>xey!=xeyThese operations are variants of the comparison operations above. The first register name is followed by the letter 'e' and another register name. Registerxwill be executed if the relation is true, and registerywill be executed if the relation is false. This is a non-portable extension.(The top two numbers are popped from the stack and compared. A one is pushed if the top of the stack is less than the second number on the stack. A zero is pushed otherwise. This is a non-portable extension.{The top two numbers are popped from the stack and compared. A one is pushed if the top of stack is less than or equal to the second number on the stack. A zero is pushed otherwise. This is a non- portable extension.!Interprets the rest of the line as a UNIX command.?A line of input is taken from the input source (usually the ter- minal) and executed.:rPop two values from the stack. The second value on the stack is stored into the arrayrindexed by the top of stack.;rPop a value from the stack. The value is used as an index into registerr. The value in this register is pushed onto the stack. Array elements initially have the value zero. Each level of a stacked register has its own array associated with it. The com- mand sequence [first] 0:a [dummy] Sa [second] 0:a 0;a p La 0;a p will print second first since the string 'second' is written in an array that is later popped, to reveal the array that stored 'first'.#Skip the rest of the line. This is a non-portable extension.

Registers have a single character namex, wherexmay be any character, including space, tab or any other special character. If extended register mode is enabled using the-xoption and the register identifierxhas the value 255, the next two characters are interpreted as a two-byte register index. The set of standard single character registers and the set of ex- tended registers do not overlap. Extended register mode is a non-portable extension.

An example which prints the first ten values ofn!: [la1+dsa*pla10>y]sy 0sa1 lyx Independent of the current input base, the command Ai will reset the input base to decimal 10.

%c (0%o) is unimplementedan undefined operation was called.stack emptyfor not enough elements on the stack to do what was asked.stack register '%c' (0%o) is emptyfor anLoperation from a stack re- gister that is empty.Runtime warning: non-zero scale in exponentfor a fractional part of an exponent that is being ignored.divide by zerofor trying to divide by zero.remainder by zerofor trying to take a remainder by zero.square root of negative numberfor trying to take the square root of a negative number.index too bigfor an array index that is larger than 2048.negative indexfor a negative array index.input base must be a number between 2 and 16for trying to set an ille- gal input base.output base must be a number greater than 1for trying to set an illegal output base.scale must be a nonnegative numberfor trying to set a negative or zero scale.scale too largefor trying to set a scale that is too large. A scale must be representable as a 32-bit unsigned number.Q command argument exceeded string execution depthfor trying to pop the recursion level more than the current recursion level.Q command requires a number >= 1for trying to pop an illegal number of recursion levels.recursion too deepfor too many levels of nested execution. The recursion level is increased by one if thexor ? operation or one of the compare operations resulting in the execution of register is execut- ed. As an exception, the recursion level is not increased if the opera- tion is executed as the last command of a string. For example, the com- mands [lax]sa 1 lax will execute an endless loop, while the commands [laxp]sa 1 lax will terminate because of a too deep recursion level.J command argument exceeded string execution depthfor trying to pop the recursion level more than the current recursion level.mark not foundfor a failed scan for an occurrence of theMoperator.

bc(1) L. L. Cherry and R. Morris, "DC - An Interactive Desk Calculator",USD:05.

The arithmetic operations of thedcutility are expected to conform to the definition listed in the bc(1) section of the IEEE Std 1003.2 ("PO- SIX.2") specification.

Thedccommand first appeared in Version 6 AT&T UNIX. A complete rewrite of thedccommand using the bn(3) big number routines first appeared in OpenBSD 3.5.

The original version of thedccommand was written by Robert Morris and Lorinda Cherry. The current version of thedcutility was written by Otto Moerbeek. MirOS BSD #10-current August 19, 2014 5

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