3.4 KiB
- AMD64 & AArch64 int initialization wrong
- Pointer arithmetic wrong
- struct initialization
- C style function pointers
- logical and do not short circuit
M2-Planet is subset of the C programming language.
Mostly by eliminating features that have yet to be proven useful in building compilers, linkers or assemblers.
AMD64 & AArch64 int initialization wrong
right now the code in cc_core.c in the function void program() simply doesn't output the correct output for AArch64 or AMD64. As the function should numerate the string global_token to determine if the leading 32bits should be 0 or 0xFFFFFFFF and output %0 or %0xFFFFFFFF accordingly.
example of failing code
#include<stdlib.h> #include<stdio.h> #include<string.h>
void write_string(char* s, FILE* f) { while(0 != s[0]) { fputc(s[0], f); s = s + 1; } }
void* empty = 0;
int main() { if (0 == empty) { write_string("Yes, is empty\n", stdout); } else { write_string("Oops, why not?\n", stdout); } return 0; }
Pointer arithmetic wrong
It isn't uncommon for complex C programs to iterate over an array using a pointer.
example of failing code
#include <stdio.h> #include <stdlib.h>
void walk_array(char** array, char** array_end) { char** i = array; while(i < array_end) { fputs(i[0], stdout); fputc('\n', stdout); i = i + 1; } }
int main() { char** array = calloc(10, sizeof(char*)); array[0] = "hello"; array[1] = "world"; array[2] = "how"; array[3] = "are"; array[4] = "you"; array[5] = "today"; array[6] = "I"; array[7] = "am"; array[8] = "doing"; array[9] = "fine"; walk_array(array, array + 10); return 0; }
work around code
#include <stdio.h> #include <stdlib.h>
#if defined(M2) #define pointer_size sizeof(char*) #else #define pointer_size 1 #endif
void walk_array(char** array, char** array_end) { char** i = array; while(i < array_end) { fputs(i[0], stdout); fputc('\n', stdout); i = i + pointer_size; } }
int main() { char** array = calloc(10, sizeof(char*)); array[0] = "hello"; array[1] = "world"; array[2] = "how"; array[3] = "are"; array[4] = "you"; array[5] = "today"; array[6] = "I"; array[7] = "am"; array[8] = "doing"; array[9] = "fine"; walk_array(array, array + (10 * pointer_size)); return 0; }
struct initialization
M2-Planet doesn't support static initialization for structs yet.
Simply because time hasn't been made available for the effort.
Patches for adding support are welcome.
C style function pointers
M2-Planet supports universal function pointer FUNCTION Simply delete the typedef and the code works fine in M2-Planet
example of failing code
#include <stdio.h> typedef int (*FUNCTION) ();
struct function { FUNCTION function; int arity; char* name; };
struct function fun_make_cell_;
int make_cell_ () { char* i = fun_make_cell_.name; while(0 != i[0]) { fputc(i[0], stdout); i = i + 1; } return fun_make_cell_.arity; }
int main () { fun_make_cell_.function = make_cell_; fun_make_cell_.arity = 2; fun_make_cell_.name = "bar\n"; fun_make_cell_.function(); }
logical and do not short circuit
Both sides of && evaluate because it hasn't been shown to be worth the effort of implementation of short-circuit logic
example of failing code
#include <stdlib.h> #include <stdio.h>
int boom() { exit(EXIT_FAILURE); }
int main(int argc, char* argv) { if((0 == argc) && boom()) { fputs("impossible code\n", stderr); } return 0; }
work around code
#include <stdlib.h> #include <stdio.h>
int boom() { exit(EXIT_FAILURE); }
int main(int argc, char* argv) { if(0 == argc) { if(boom())fputs("impossible code\n", stderr); } return 0; }