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Don't no too much about C, but I read that it explicitly doesn't allow such things.
Yes, something like this should workvoid (*app)() = (void(*))0x123456;and then laterapp();I can't test this right now, but I'm pretty sure the above would jump to addres 0x123456.
The most obvious legal way to do this is to use a table of function pointers.
Well the gcc extension is as portable as gcc is. If you keep your dubious computed branch target code to just one translation unit, you could always make it an exception in your makefile and have everything else all nice and ANSI.
No, that's a function pointer which will invoke the calling convention (saving registers etc) which would add a lot of overhead a threaded code Virtual Machine...
Oh, then I misunderstood your question. :-)
If you're just writing for ARM and testing on x86, couldn't you use a conditionally-compiled bit of assembler like:Code: [Select]#ifdef ARMasm { /* whatever */}#elseasm { /* x86 equivalent */}#endifor somesuch?
#ifdef ARMasm { /* whatever */}#elseasm { /* x86 equivalent */}#endif
Necessarily it is not saving the registers for every function call. It is platform specific...
That depends. If shovel it all into the same translation unit so it can see the scope of everything whilst it is compiling, you'd be surprised...
protothreads / coroutines. But mostly, C was not built to do what you want to do. Look at a lot of Forth interpreters and see how they do it, they pioneered the threaded code model, but mostly the ones I've seen use this method are written in assembler.
If it helps, I've built a "virtual processor" using function tables / giant switch case depending on compiler settings as an experiment. Can send you the source if it helps.PM me if you are interested.
Is it the one that has a test virtual program to generate the Mandelbrot set as a PPM file?
Then maybe the version you have is old? This one even had a whole bunch of evil C macros that allowed the VM code to be written within the C source:Code: [Select]void nativeAllocBuffer(VMCore* vm){ // width/height in r2/r3 // return buffer in r1 int w = vm->getReg(_r2).s32(); int h = vm->getReg(_r3).s32(); vm->getReg(_r1).pU8() = new uint8[w*h]; printf("Allocated buffer [%d x %d]\n", w, h);}void nativeFreeBuffer(VMCore* vm){ // expects buffer in r1 delete[] vm->getReg(_r1).pCh(); vm->getReg(_r1).pCh() = 0; printf("Freed buffer\n");}void nativeWriteBuffer(VMCore* vm){ // writes buffer in r1 to filename in r4 // expects width/height in r2/r3 const char* fileName = vm->getReg(_r16).pCh(); int w = vm->getReg(_r2).s32(); int h = vm->getReg(_r3).s32(); if (fileName) { FILE *f = fopen(fileName, "wb"); fprintf(f, "P5\n%d\n%d\n255\n", w, h); fwrite(vm->getReg(_r1).pCh(), 1, w*h, f); fclose(f); printf("Wrote buffer '%s'\n", fileName); }}void nativePrintCoords(VMCore* vm){ printf( "Coords %4d, %4d (%.6f, %.6f)\n", (int)vm->getReg(_r7).s32(), (int)vm->getReg(_r5).s32(), vm->getReg(_r9).f32(), vm->getReg(_r4).f32() );}_VM_CODE(makeFractal){ // r1 = pixel data address // r2 = width in pixels // r3 = height in pixels // r4 = cY (float pos, starting at yMin) // r5 = y (int) pixel // r6 = xMin (float) // r7 = cX (float pos, starting at xMin) // r8 = fStep // r9 = x (int) pixel // r10 = iStep (1) _save (_mr1) // 2 : save r1 _ldq (0, _r5) // 1 : y (r5) = 0 _ld_16_i32 (255, _r10) // 2 : max iters // y-loop _ldq (0, _r9) // 1 : x = 0 _move_32 (_r6, _r7) // 1 : cX = xMin // x-loop do { _move_32 (_r7, _r11) // 1 : zx = cX _move_32 (_r4, _r12) // 1 : zy = cY _ldq (0, _r13) // 1 : n = 0 // do { _move_32 (_r11, _r14) // 1 _mul_f32 (_r11, _r14) // 1 : zx2 = zx*zx _move_32 (_r12, _r15) // 1 _mul_f32 (_r12, _r15) // 1 : zy2 = zy*zy _move_32 (_r7, _r16) // 1 : new_zx = cX _add_f32 (_r14, _r16) // 1 : new_zx += zx2 _sub_f32 (_r15, _r16) // 1 : new_zx -= zy2 _add_f32 (_r15, _r14) // 1 : r14 = zx*zx + zy*zy (for loop test) _move_32 (_r11, _r15) // 1 : tmp = zx _mul_f32 (_r12, _r15) // 1 : tmp *= zy _add_f32 (_r15, _r15) // 1 : tmp += tmp2 _add_f32 (_r4, _r15) // 1 : tmp += cY (tmp = 2*zx*zy+cY) _move_32 (_r15, _r12) // 1 : zy = tmp _move_32 (_r16, _r11) // 1 : zx = new_zx _addi_16 (1, _r13) // 2 : n++ _ld_32_f32 (4.0f, _r16) // 3 _bgr_f32 (_r14, _r16, 2) // 2 _bls_32 (_r13, _r10, -23) // 2 _mul_u16 (_r13, _r13) // 1 _st_ripi_8 (_r13, _r1) // 1 : out = n _add_f32 (_r8, _r7) // 1 : cX += fStep _addi_16 (1, _r9) // 2 : x += iStep _bls_32 (_r9, _r2, -(6+23+3+1)) // 2 : } while (x < width) _add_f32 (_r8, _r4) // 1 : cY += fStep _addi_16 (1, _r5) // 2 : y += iStep _bls_32 (_r5, _r3, -(5+5+6+23+1)) // 2 : } while (y < height) _restore (_mr1) // 1 _ret};_VM_CODE(calculateRanges){ // calculates xMin in r6, xMax in r7, step in r8 _move_32 (_r5, _r6) _sub_f32 (_r4, _r6) // r6 = r5-r4 (total y range) _s32to_f32 (_r2, _r7) // r7 = (float) r2 _move_32 (_r7, _r9) _mul_f32 (_r6, _r7) // r7 *= r6 _s32to_f32 (_r3, _r6) // r6 = (float) r3 _div_f32 (_r6, _r7) // r7 /= r6 _move_32 (_r7, _r8) _div_f32 (_r9, _r8) _ld_32_f32 (0.75f, _r6) _sub_f32 (_r7, _r6) _add_f32 (_r6, _r7) _ret};_VM_CODE(virtualProgram) // a vm function{ _ld_16_i16 (512, _r2) _ld_16_i16 (512, _r3) _calln (nativeAllocBuffer) _ld_32_f32 (-1.25f, _r4) // yMin _ld_32_f32 (1.25f, _r5) // yMax _call (calculateRanges) _call (makeFractal) _lda ("framebuffer.pgm", _r16) _calln (nativeWriteBuffer) _calln (nativeFreeBuffer) _ret};
void nativeAllocBuffer(VMCore* vm){ // width/height in r2/r3 // return buffer in r1 int w = vm->getReg(_r2).s32(); int h = vm->getReg(_r3).s32(); vm->getReg(_r1).pU8() = new uint8[w*h]; printf("Allocated buffer [%d x %d]\n", w, h);}void nativeFreeBuffer(VMCore* vm){ // expects buffer in r1 delete[] vm->getReg(_r1).pCh(); vm->getReg(_r1).pCh() = 0; printf("Freed buffer\n");}void nativeWriteBuffer(VMCore* vm){ // writes buffer in r1 to filename in r4 // expects width/height in r2/r3 const char* fileName = vm->getReg(_r16).pCh(); int w = vm->getReg(_r2).s32(); int h = vm->getReg(_r3).s32(); if (fileName) { FILE *f = fopen(fileName, "wb"); fprintf(f, "P5\n%d\n%d\n255\n", w, h); fwrite(vm->getReg(_r1).pCh(), 1, w*h, f); fclose(f); printf("Wrote buffer '%s'\n", fileName); }}void nativePrintCoords(VMCore* vm){ printf( "Coords %4d, %4d (%.6f, %.6f)\n", (int)vm->getReg(_r7).s32(), (int)vm->getReg(_r5).s32(), vm->getReg(_r9).f32(), vm->getReg(_r4).f32() );}_VM_CODE(makeFractal){ // r1 = pixel data address // r2 = width in pixels // r3 = height in pixels // r4 = cY (float pos, starting at yMin) // r5 = y (int) pixel // r6 = xMin (float) // r7 = cX (float pos, starting at xMin) // r8 = fStep // r9 = x (int) pixel // r10 = iStep (1) _save (_mr1) // 2 : save r1 _ldq (0, _r5) // 1 : y (r5) = 0 _ld_16_i32 (255, _r10) // 2 : max iters // y-loop _ldq (0, _r9) // 1 : x = 0 _move_32 (_r6, _r7) // 1 : cX = xMin // x-loop do { _move_32 (_r7, _r11) // 1 : zx = cX _move_32 (_r4, _r12) // 1 : zy = cY _ldq (0, _r13) // 1 : n = 0 // do { _move_32 (_r11, _r14) // 1 _mul_f32 (_r11, _r14) // 1 : zx2 = zx*zx _move_32 (_r12, _r15) // 1 _mul_f32 (_r12, _r15) // 1 : zy2 = zy*zy _move_32 (_r7, _r16) // 1 : new_zx = cX _add_f32 (_r14, _r16) // 1 : new_zx += zx2 _sub_f32 (_r15, _r16) // 1 : new_zx -= zy2 _add_f32 (_r15, _r14) // 1 : r14 = zx*zx + zy*zy (for loop test) _move_32 (_r11, _r15) // 1 : tmp = zx _mul_f32 (_r12, _r15) // 1 : tmp *= zy _add_f32 (_r15, _r15) // 1 : tmp += tmp2 _add_f32 (_r4, _r15) // 1 : tmp += cY (tmp = 2*zx*zy+cY) _move_32 (_r15, _r12) // 1 : zy = tmp _move_32 (_r16, _r11) // 1 : zx = new_zx _addi_16 (1, _r13) // 2 : n++ _ld_32_f32 (4.0f, _r16) // 3 _bgr_f32 (_r14, _r16, 2) // 2 _bls_32 (_r13, _r10, -23) // 2 _mul_u16 (_r13, _r13) // 1 _st_ripi_8 (_r13, _r1) // 1 : out = n _add_f32 (_r8, _r7) // 1 : cX += fStep _addi_16 (1, _r9) // 2 : x += iStep _bls_32 (_r9, _r2, -(6+23+3+1)) // 2 : } while (x < width) _add_f32 (_r8, _r4) // 1 : cY += fStep _addi_16 (1, _r5) // 2 : y += iStep _bls_32 (_r5, _r3, -(5+5+6+23+1)) // 2 : } while (y < height) _restore (_mr1) // 1 _ret};_VM_CODE(calculateRanges){ // calculates xMin in r6, xMax in r7, step in r8 _move_32 (_r5, _r6) _sub_f32 (_r4, _r6) // r6 = r5-r4 (total y range) _s32to_f32 (_r2, _r7) // r7 = (float) r2 _move_32 (_r7, _r9) _mul_f32 (_r6, _r7) // r7 *= r6 _s32to_f32 (_r3, _r6) // r6 = (float) r3 _div_f32 (_r6, _r7) // r7 /= r6 _move_32 (_r7, _r8) _div_f32 (_r9, _r8) _ld_32_f32 (0.75f, _r6) _sub_f32 (_r7, _r6) _add_f32 (_r6, _r7) _ret};_VM_CODE(virtualProgram) // a vm function{ _ld_16_i16 (512, _r2) _ld_16_i16 (512, _r3) _calln (nativeAllocBuffer) _ld_32_f32 (-1.25f, _r4) // yMin _ld_32_f32 (1.25f, _r5) // yMax _call (calculateRanges) _call (makeFractal) _lda ("framebuffer.pgm", _r16) _calln (nativeWriteBuffer) _calln (nativeFreeBuffer) _ret};
I can send you this version. It basically is a bit crap in that it compiles to a single executable containing the embedded test. The reason being, the final target was for a library which included all the necessary loading/linking stuff. It should compile on any posix compliant system.
