Added environment routines

git-svn-id: svn://svn.cc65.org/cc65/trunk@3483 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/common/getenv.s

@@ -0,0 +1,46 @@
+;
+; Ullrich von Bassewitz, 2005-04-21
+;
+; char* __fastcall__ getenv (const char* name);
+;
+; Beware: putenv() knows about zero page usage in this module!
+;
+
+        .export _getenv
+        .import __environ, __envcount
+        .import searchenv
+        .import return0
+        .import ptr1:zp, ptr3:zp, tmp1:zp
+
+.code
+
+;----------------------------------------------------------------------------
+; getenv()
+
+.proc   _getenv
+
+        sta     ptr1
+        stx     ptr1+1                  ; Save name
+
+; Search for the string in the environment. searchenv will set the N flag if
+; the string is not found, otherwise X contains the index of the entry, ptr3
+; contains the entry and Y the offset of the '=' in the string.
+
+        jsr     searchenv
+        bpl     found
+        jmp     return0                 ; Not found, return NULL
+
+; Found the entry. Calculate the pointer to the right side of the environment
+; variable. Because we want to skip the '=', we will set the carry.
+
+found:  ldx     ptr3+1                  ; High byte of result
+        tya
+        sec
+        adc     ptr3
+        bcc     @L9
+        inx
+@L9:    rts
+
+.endproc
+
+