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mateuszvis |
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/*
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* routines used to manipulate the environment block
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*/
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#include <i86.h>
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#include <string.h>
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#include "env.h"
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/* looks for varname in environment block and returns a far ptr to it if
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* found, NULL otherwise. varname MUST be in upper-case and MUST be terminated
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* by either a = sign or a NULL terminator */
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char far *env_lookup(unsigned short env_seg, const char *varname) {
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char far *env = MK_FP(env_seg, 0);
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int i;
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for (;;) {
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/* is this it? */
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for (i = 0;; i++) {
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if ((varname[i] == '=') || (varname[i] == 0)) {
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if (env[i] == '=') return(env); /* FOUND! */
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break; /* else look for next string */
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}
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if (varname[i] != env[i]) break;
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}
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/* move env to end of current string */
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while (*env != 0) env++;
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/* if there's another trailing zero, then that is the end of environment */
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env++;
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if (*env == 0) return(NULL);
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}
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}
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/* returns the size, in bytes, of the allocated environment block */
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unsigned short env_allocsz(unsigned short env_seg) {
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unsigned short far *mcbsz = MK_FP(env_seg - 1, 3); /* block size is a word at offset +3 in the MCB */
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return(*mcbsz * 16); /* return size in bytes, not paragraphs */
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}
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/* remove a variable from environment, if present. returns 0 on success, non-zero if variable not found */
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int env_dropvar(unsigned short env_seg, const char *varname) {
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unsigned short blocksz, traillen;
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unsigned short len;
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char far *varptr = env_lookup(env_seg, varname);
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/* if variable not found in environment, quit now */
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if (varptr == NULL) return(-1);
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for (len = 0; varptr[len] != 0; len++); /* compute length of variable (without trailing null) */
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blocksz = env_allocsz(env_seg); /* total environment size */
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traillen = blocksz - (FP_OFF(varptr) + len + 1); /* how much bytes are present after the variable */
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_fmemset(varptr, 0, len); /* zero out the variable */
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if (traillen != 0) {
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_fmemmove(varptr, varptr + len + 1, traillen); /* move rest of memory */
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}
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return(0);
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}
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/* Writes a variable to environment block. The variable must in the form
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* "VARNAME=value". If variable is already present in the environment block,
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* then the value will be updated. If the new value is empty, then the
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* existing variable (if any) is removed.
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* VARNAME *MUST* be all-uppercase.
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*
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* This function returns:
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* ENV_SUCCESS = success
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* ENV_NOTENOM = not enough available space in memory block
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* ENV_INVSYNT = invalid syntax
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*/
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int env_setvar(unsigned short env_seg, const char *v) {
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unsigned short envlen;
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unsigned short envfree;
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unsigned short vlen, veqpos;
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char far *env = MK_FP(env_seg, 0);
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/* remove variable from environment, if already set */
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env_dropvar(env_seg, v);
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/* compute v length and find the position of the eq sign */
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veqpos = 0xffff;
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for (vlen = 0; v[vlen] != 0; vlen++) {
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if (v[vlen] == '=') {
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if (veqpos != 0xffff) return(ENV_INVSYNT); /* equal sign is forbidden in value */
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veqpos = vlen;
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}
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}
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/* if variable empty, stop here */
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if (veqpos == vlen - 1) return(ENV_SUCCESS);
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/* compute current size of the environment */
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for (envlen = 0; env[envlen] != 0; envlen++) {
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while (env[envlen] != 0) envlen++; /* consume a string */
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}
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/* compute free space available in environment */
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envfree = env_allocsz(env_seg);
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envfree -= envlen;
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envfree -= 1; /* 1 byte for the environment's NULL terminator */
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/* do I have enough env space for the new var? */
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if (envfree < vlen + 1) return(ENV_NOTENOM);
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/* write the new variable (with its NULL terminator) to environment tail */
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_fmemcpy(env + envlen, v, vlen + 1);
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/* add the environment's NULL terminator */
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env[envlen + vlen + 1] = 0;
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return(ENV_SUCCESS);
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}
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