Os/9 emulator -mac -macos -macos910/25/2022 For each digit it does one multiplication by the base and an addition of the next digit. The standard method for converting the human-readable form of a number to its internal representation is just Horner’s method of evaluating the polynomial that the human-readable form represents, where the digits are the coefficients and x is the base. We’ll ignore signs, decimal places, and exponents for now, and just look at parsing non-negative integers. Why the time difference between 65535, &HFFFF, and &O177777? It has to do with how that conversion is done. Every time through those loops the Color BASIC interpreter determines that the digit string “65535” (not in quotes in the source code, of course) still corresponds to the value 65535–honest! That last part is the reason for the times shown in “ Make BASIC Fast Again, Part 2“. as part of that parsing, you have to convert constants from the text format they were entered in to the internal format (a five-byte binary floating point number) every time you execute the statement.expressions are left in their original form, so you get to reparse them, looking at the operators and their precedence and the parentheses to figure out what to do and in what order, every time you execute the statement.identifiers aren’t replaced with pointers to the matching symbol table entries, so you get to look up your variables every time you execute the statement.It also lets you execute the statement, but… This form lets you implement GOTO and GOSUB, lets you regenerate the original source for LIST (fill a buffer with the line number converted back to printed form, followed by the text of the line with the codes converted back to keywords or function names, and you’re good to go). the text of the line, except that BASIC keywords and built-in function names are replaced with one- (for keywords) or two- (for built-in functions) byte codes.a value indicating the length of the tokenized statement.a two-byte integer field holding the line number.Each source line is converted into a “tokenized” form that has Os/9 emulator mac macos macos9 code#Tight memory constraints demanded algorithms that minimized code and data size, often at the expense of time.Īllen’s series will hint at more of these the first two, though, have to do with how the lines of BASIC code are stored in RAM. Later on, they wrote versions for many other personal computers, probably keeping the same overall structure but customizing to the target’s features and of course rewriting for new target processors. There was a version that would run with just 4K of RAM, and one for systems with 8K of RAM. Microsoft started out with a BASIC interpreter for the 8080-based MITS Altair. How Color BASIC and other Microsoft BASICs of the era do things What’s that? Well, first a little history. To avoid these issues without a speed penalty but with other advantages as well, consider BASIC09. One can write a program to do some of these modifications to relatively clean code, but when it comes time to debug, you must work with the munged version. Unfortunately, those modifications play havoc with code legibility. Modify your code to work around the limitations the BASIC interpreter inherited from its origins on systems with extremely limited resources. Allen Huffman is graciously sharing ways to speed up programs written for the family of Microsoft BASIC interpreters common on personal computers of the time that interests us, including the various flavors of Color BASIC.
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