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Wrote explanation

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Koichi Nakamura 2020-12-30 22:38:27 +09:00
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core.fs
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@ -19,4 +19,87 @@ l!
\ planckforth -
\ Copyright (C) 2020 nineties
\ This project aims to create a full-fledged Forth interpreter
\ by bootstrapping from hand-written tiny ELF binary.
\ In the 1st stage, only single character words are registered
\ in the dictionary.
\ List of builtin words:
\ 'Q' ( -- ) Exit the process
\ 'C' ( -- n ) The size of Cells
\ 'h' ( -- addr ) The address of 'here' cell
\ 'l' ( -- addr ) The address of 'latest' cell
\ 'k' ( -- c ) Read character
\ 't' ( c -- ) Print character
\ 'j' ( -- ) Unconditional branch
\ 'J' ( a -- ) Jump if a == 0
\ 'f' ( c -- xt ) Get execution token of c
\ 'x' ( xt -- ... ) Run the execution token
\ '@' ( addr -- a ) Load value from addr
\ '!' ( a addr -- ) Store value to addr
\ '?' ( addr -- c ) Load byte from addr
\ '$' ( c addr -- ) Store byte to addr
\ 'd' ( -- addr ) Get data stack pointer
\ 'D' ( addr -- ) Set data stack pointer
\ 'r' ( -- addr ) Get return stack pointer
\ 'R' ( addr -- ) Set return stack pointer
\ 'i' ( -- addr ) Get the interpreter function
\ 'e' ( -- ) Exit current function
\ 'L' ( -- a ) Load immediate
\ 'S' ( -- addr len) Load string literal
\ '+' ( a b -- c ) c = (a + b)
\ '-' ( a b -- c ) c = (a - b)
\ '*' ( a b -- c ) c = (a * b)
\ '/' ( a b -- c ) c = (a / b)
\ '%' ( a b -- c ) c = (a % b)
\ '&' ( a b -- c ) c = (a & b)
\ '|' ( a b -- c ) c = (a | b)
\ '^' ( a b -- c ) c = (a ^ b)
\ '<' ( a b -- c ) c = (a < b)
\ '=' ( a b -- c ) c = (a == b
\ The 1st stage interpreter repeats execution of k, f and x.
\ There is no concept such as IMMEDIATE mode yet.
\ There following line is an example program of planckforth
\ which prints "Hello World!\n"
\ --
\ kHtketkltkltkotk tkWtkotkrtkltkdtk!tk:k0-tQ
\ --
\ This code repeats that 'k' reads a character and 't' prints it.
\ Note that ':' (58) minus '0' (48) is '\n' (10).
\ The structure of the dictionary is sames as many Forth implementation.
\ +------+----------+---------+------------+---------------+
\ | link | len+flag | name... | padding... | code field ...|
\ +------+----------+---------+------------+---------------+
\ - link pointer to the previous entry (CELL byte)
\ - length of the name (5 bits)
\ - immediate flag (1 bit)
\ - smuege flag (1 bit)
\ - unused bit (1 bit)
\ - characters of the name (N bits)
\ - padding to align CELL boundary if necessary.
\ - codewords and datawords (CELL-bye aligned)
\ The code group at the beginning of this file
\ defines ' ' and '\n' as no-op operation and
\ '\' to read following characters until '\n'.
\ Since I couldn't write a comment at the beginning,
\ I repost the definition of '\' for explanation.
\ --
\ h@ ( save addr of new entry )
\ l@ h@!h@C+h! ( set link pointer. *here++ = latest )
\ k1k0-h@$ k\h@k1k0-+! h@C+h! ( write the name '\' and its length )
\ i h@!h@C+h! ( docol )
\ kkf h@!h@C+h! ( key )
\ kLf h@!h@C+h! ( lit )
\ k:k0- h@!h@C+h! ( '\n' )
\ k=f h@!h@C+h! ( = )
\ kJf h@!h@C+h! ( branch )
\ k0k5-C* h@!h@C+h! ( -5*CELL )
\ kef h@!h@C+h! ( exit )
\ l! ( set latest to this new entry. )
\ --
Q