Here is our latest incarnation of simple-forth, a forth interpreter written in C.
This time we add floating point arithmetic capabilities. There are two basic ways to incorporate floating point capabilities. One is using the same integer stack and the other is using a separate foating point stack.
We use a separate floating point stack with maximum 32 elements. in our newest version shown below for simplicity. The built-in integer stack is 32 bits wide. Floating point numbers in our interpreter are 64 bit wide. The current stack element index is indicated by FP. The basic floating point operations are f+, f-, f*, f/ these Forth words are the equivalent floating point words corresponding to the built-in basic + - * / operator words
:
/*
file simple-forth-0.0.3.c
author Dr. Ernesto P. Adorio
UPDEPP (University of the Philippines,
Extension Program in Pampanga
Clarkfield, Pampanga
email ernesto.adorio@gmail.com
version 0.0.1 January 14, 2012 basic interpreter.
0.0.2 January 16, 2012 interactivity added.
0.0.3 January 25, 2012 basic floating point.
*/
#include
#include
#include
#include
enum {E_STACKUNDERFLOW, E_FSTACKUNDERFLOW} ERRCODES;
enum {L_EMIT, L_DOT,L_DOTT, L_SPACE, L_ADD, L_SUB, L_MUL, L_DIV, L_DROP, L_INT32, L_CR,
L_FNUM, L_FPLUS, L_FSUB, L_FMUL, L_FDIV, L_FDOT, L_FDOTT, L_FDROP,
L_BYE, L_EOS,L_ERROR} OPCODES;
const char *stdwords[] = { "emit", ".", ".t", "space", "+", "-", "*", "/", "drop", "int32", "cr",
"fnum", "f+", "f-", "f*" ,"f/", "f.","f.t","fdrop",
"bye",
"\n",
};
// "int32" and "fnum" are dummies.
#define MAXSTKLEN 32
#define MAXFSTKLEN 32
#define MAXTOKENLEN 128
int LENSTDWORDS = sizeof(stdwords)/sizeof(stdwords[0]);
char LINEBUFFER[256];
char *goodbye= "bye";
int ERRCODE = 0;
int SP = -1; /* stack pointer index */
int stack[MAXSTKLEN];
int opcode;
char *tokstart;
char *tokend;
int FP = -1; /* floating point stack index */
double fstack[MAXFSTKLEN];
int numbertype(char *s)
{
/*
Returns
0 - not a number!
1 - an integer
2 - a floating point number
*/
char *t = s;
while (isspace(*t)) t++;
if (*t == '\0') return 0;
if (*t == '+' || *t == '-') t++;
if (*t == '\0') return 0;
while (isdigit(*t)) t++;
if (*t == '\0') {
return 1; // an integer!
}
if (*t == '.') t++;
while (isdigit(*t)) t++;
if (*t == '\0') return 2;
if (*t == 'e') t++;
if (*t == '\0') return 0; // error!
if (*t == '+' || *t == '-') t++;
if (*t == '\0') return 0; // error!
while (isdigit(*t)) t++;
if (*t == '\0') return 2; // a floating point number!
return 0; // not an integer or floating point.
}
int eval(int opcode)
{
/* Evaluate opcode */
switch (opcode){
case L_EMIT:
//@@printf("opcode L_EMIT %s %d\n", tokstart, SP);
if (SP < 0) {
ERRCODE = E_STACKUNDERFLOW;
} else {
printf ("%c", stack[SP--]);
}
break;
case L_DOT:
printf("opcode L_EMIT %s %d\n", tokstart, SP);
if (SP < 0) {
ERRCODE = E_STACKUNDERFLOW;
printf("%s", "underflow!");
} else {
printf ("%d", stack[SP--]);
}
break;
case L_DOTT:
//@@printf("opcode L_EMIT %s %d\n", tokstart, SP);
if (SP < 0) {
ERRCODE = E_STACKUNDERFLOW;
printf("%s", "underflow!");
} else {
printf ("%d", stack[SP]);
}
break;
case L_SPACE:
printf ("%c", 32);
break;
case L_ADD:
//printf("opcode L_ADD %s\n", tokstart);
if (SP <= 0) {
ERRCODE = E_STACKUNDERFLOW;
printf("%s", "underflow!");
break;
}
stack[SP-1] += stack[SP];
SP--;
break;
case L_SUB:
//printf("opcode L_SUB %s\n", tokstart);
if (SP <= 0) {
ERRCODE = E_STACKUNDERFLOW;
printf("%s", "underflow!");
break;
}
stack[SP-1] -= stack[SP];
SP--;
break;
case L_MUL:
//printf("opcode L_MUL %s\n", tokstart);
if (SP <= 0) {
ERRCODE = E_STACKUNDERFLOW;
printf("%s", "underflow!");
break;
}
stack[SP-1] *= stack[SP];
SP--;
break;
case L_DIV:
//printf("opcode L_DIV %s\n", tokstart);
if (SP <= 0) {
ERRCODE = E_STACKUNDERFLOW;
printf("%s", "underflow!");
break;
}
stack[SP-1] /= stack[SP];
SP--;
break;
case L_INT32:
//printf("opcode L_INT32 %s\n",tokstart);
stack[++SP]= atoi(tokstart);
// printf("@@@ pushing an integer!");
break;
case L_DROP:
//printf("opcode L_DROP %s \n", tokstart);
SP=SP -1;
break;
case L_CR:
// printf("opcode L_CR %s \n", tokstart);
printf("\n");
break;
/* simple floating point features */
case L_FNUM:
//printf("floating point number %s\n",tokstart);
fstack[++FP]= atof(tokstart);
break;
case L_FPLUS:
if (FP <= 0) {
ERRCODE = E_FSTACKUNDERFLOW;
printf("%s", "fstack underflow!");
break;
}
fstack[FP-1] += fstack[FP];
FP--;
break;
case L_FSUB:
if (FP <= 0) {
ERRCODE = E_FSTACKUNDERFLOW;
printf("%s", "fstack underflow!");
break;
}
fstack[FP-1] -= fstack[FP];
FP--;
break;
case L_FMUL:
if (FP <= 0) {
ERRCODE = E_FSTACKUNDERFLOW;
printf("%s", "fstack underflow!");
break;
}
fstack[FP-1] *= fstack[FP];
FP--;
break;
case L_FDIV:
if (FP <= 0) {
ERRCODE = E_FSTACKUNDERFLOW;
printf("%s", "fstack underflow!");
break;
}
fstack[FP-1] /= fstack[FP];
FP--;
break;
case L_FDOT:
printf("opcode FDOT %s\n", tokstart);
if (FP < 0) {
ERRCODE = E_FSTACKUNDERFLOW;
printf("%s", "underflow!");
} else {
printf ("%f", fstack[FP--]);
}
break;
case L_FDOTT:
//@@printf("opcode L_EMIT %s %d\n", tokstart, SP);
if (SP < 0) {
ERRCODE = E_FSTACKUNDERFLOW;
printf("%s", "underflow!");
} else {
printf ("%f", fstack[FP]);
}
break;
case L_BYE:
printf("Terminating... ");
break;
default:
;
break;
}
}
void nexttoken()
{
tokstart = tokend;
//@ printf("inside nexttoken [%s]", tokstart);
/* ignore leading white spaces */
while (isspace(*tokstart)) tokstart++;
/* find terminating space of end of string */
tokend = tokstart;
while (!isspace(*tokend) && *tokend != '\0') tokend++;
/* string terminator */
if (*tokend != '\0') {
*tokend = '\0';
tokend ++;
}
/* get opcode */
opcode = -1;
if (tokend == tokstart) {
opcode = L_EOS;
return;
}
//@@@ printf("token [%s]\n", tokstart);
for (int i =0; i < LENSTDWORDS; i++) {
if (strcmp(stdwords[i], tokstart) == 0){
opcode = i;
break;
}
}
if (opcode != -1) {
return;
}
int ntype = numbertype(tokstart);
if (ntype == 1){
/* is this a number ?*/
opcode = L_INT32;
} else if (ntype == 2) {
opcode = L_FNUM;
} else if (opcode == -1){
opcode = L_ERROR;
};
}
int main(){
while (1) {
printf("> ");
if (fgets(LINEBUFFER, 250, stdin)!= NULL) {
tokend=LINEBUFFER;
} else {
tokend= goodbye;
}
while (1) {
nexttoken();
eval(opcode);
if (opcode == L_BYE) {
return 0;
}
if (opcode ==L_EOS) {
break;
}
if (ERRCODE != 0) {
printf("ERRORCODE [%d]", ERRCODE);
break;
};
}
}
printf("\n");
return 0;
}
Here is compilation and a simple execution run.
gcc simple-forth-0.0.3.c -g -std=c99 -o simple-forth
toto@toto-Aspire-4520:~/Blogs/my-other-life-as-programmer/forth$ ./simple-forth
> 23.34 -56.12 f* f.
-1309.840800> bye
Terminating...
Dont forget: a floating point number has a comma or an exponent in our simple-forth implementation.
