Added environment routines

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

libsrc/common/searchenv.s

@@ -0,0 +1,84 @@
+;
+; Ullrich von Bassewitz, 2005-04-21
+;
+; Search the environment for a string.
+;
+
+        .export searchenv, copyenvptr
+        .import __environ, __envcount
+        .import ptr1:zp, ptr2:zp, ptr3:zp
+
+.code
+
+;----------------------------------------------------------------------------
+; searchenv:
+;
+; ptr1 must contain the string to search for. On exit, the N flag will tell
+; if the entry was found, and X will contain the index of the environment
+; string in the environment (a negative value if the entry was not found).
+; On success, ptr3 will contain the entry and Y the offset of the '=' within
+; the string.
+
+.proc   searchenv
+
+; Copy the pointer to the environment to the zero page
+
+	jsr	copyenvptr
+
+; Loop over all environment entries trying to find the requested one.
+
+        ldx     __envcount
+@L0:    dex
+        bmi     @L9                     ; Out of entries
+
+; Since the maximum number of entries is 64, the index can only be 63, so
+; the following shift cannot overflow and the carry is clear.
+
+        txa
+        asl     a                       ; Mul by two for word access
+        tay
+        lda     (ptr2),y
+        sta     ptr3
+        iny
+        lda     (ptr2),y
+        sta     ptr3+1
+
+; ptr1 points to name, ptr3 points to the next environment entry. Compare the
+; two. The following loop limits the length of name to 255 bytes.
+
+        ldy     #$00
+@L1:    lda     (ptr1),y
+        beq     @L2                     ; Jump on end of name
+        cmp     (ptr3),y
+        bne     @L0                     ; Next environment entry
+        iny
+        bne     @L1
+
+; End of name reached, check if the environment entry contains a '=' char
+
+@L2:    lda     (ptr3),y
+        cmp     #'='
+        bne     @L0                     ; Next environment entry
+
+; Done. The function result is in X and the N flag is set correctly.
+
+@L9:    rts
+
+.endproc
+
+
+;----------------------------------------------------------------------------
+; copyenvptr: Copy _environ to ptr2
+;
+
+.proc	copyenvptr
+
+        lda     __environ
+        sta     ptr2
+        lda     __environ+1
+        sta     ptr2+1
+	rts
+
+.endproc
+
+