OT: Altair32: C arrays and pointers

It was thus said that the Great Richard A. Cini, Jr. once stated: Okay, as one of the few token C programmers here, I'll take a shot at this. I'll give several solutions of varying amount of portability and speed, so pick wisely 8-) The code is ANSI C, which was passed in 1989, making it on topic for this group 8-P The following assumes an 8-bit character, 2 character in a short (most modern machines), either big endian or little endian (you need to define LITTLE_END): #include <limits.h> /*--------------------------------------------- ; if Intel based, set to 1, otherwise (say, for ; Motorola systems) set to 0 ;---------------------------------------------*/ #define LITTLE_END 1 #if CHAR_BIT != 8 # error No 8bit bytes supported on this system #else typedef unsigned char byte; #endif #if (USHRT_MAX != 65535UL) # error No 16bit type supported on this system #else typedef unsigned short word; #endif union defregs { byte b[2]; word w; } regs[4]; /* AF , BC, DE, HL */ #if LITTLE_END # define A regs[0].1[1] # define F regs[0].l[0] # define B regs[1].l[1] # define C regs[1].l[0] # define D regs[2].l[1] # define E regs[2].l[0] # define H regs[3].l[1] # define L regs[3].l[0] #else # define A regs[0].l[0] # define F regs[0].l[1] # define B regs[1].l[0] # define C regs[1].l[1] # define D regs[2].l[0] # define E regs[2].l[1] # define H regs[3].l[0] # define L regs[3].l[1] #endif #define BC regs[1].w #define DE regs[2].w #define HL regs[3].w You now have an easier way to reference the registers, the following code: Can be replaced with: switch((u & RP_MASK) >> 4) { case 2: /* HL */ HL++; break; /* other cases */ } To increment a register pair and check for carry (say, BC): unsigned long tmp; tmp = BC; tmp++; if (tmp > USHRT_MAX) { /* set carry flag */ } BC = tmp & 0xFFFFul; The more portable, but slower method (and not dependant upon endianness) is: #include <limits.h> typedef unsigned char byte; byte regs[8]; #define A regs[0] #define F regs[1] #define B regs[2] #define C regs[3] #define D regs[4] #define E regs[5] #define H regs[6] #define L regs[7] #define rBC ( ((B) << 8) | (C) ) #define rDE ( ((D) << 8) | (E) ) #define rHL ( ((H) << 8) | (L) ) /*------------------------------------------------------------ ; The following macros evaluate the parameter more than once. ; be careful on how you use these. Beware of side effects! ;------------------------------------------------------------*/ #define wBC(w) (B) = ((w) >> 8) & 0xFF) ; (C) = ((w) & 0xFF) #define wDE(w) (D) = ((w) >> 8) & 0xFF) ; (E) = ((w) & 0xFF) #define wHL(w) (H) = ((w) >> 8) & 0xFF) ; (L) = ((w) & 0xFF) switch((u & RP_MASK) >> 4) { unsigned int tmp; case 2: /* HL */ tmp = rHL + 1; wHL(tmp); break; /* other cases */ } /*------------------------------------- ; That carry thang ... ;--------------------------------------*/ unsigned long tmp; tmp = BC; tmp++; if (tmp > USHRT_MAX) { /* set carry flag */ } wBC(tmp); Sigh. I've been programming in C for waaaaay too long 8-) -spc (Sorry about the C code ... )