Source code in the fbsl programming language

Function StrRev1(ByVal $p1)
	dim $b = ""
	REPEAT len(p1)
		b = b & RIGHT(p1,1)
		p1 = LEFT(p1,LEN(p1)-1)
	END REPEAT
	return b
End Function


Function StrRev2(ByVal $p1)
	dim $b = "", %i
	for i = len(p1) DOWNTO 1
		b = b & MID(p1,i,1)
	next
	return b
End Function


Function StrRev3( $s )
	FOR DIM x = 1 TO LEN(s) \ 2
		PEEK(@s + LEN - x, $1)
		POKE(@s + LEN - x, s{x})(@s + x - 1, PEEK)
	NEXT
	RETURN s
end function


DynC StringRev($theString) As String
   void rev(char *str)
   {
		int len = strlen(str);
		char *HEAD = str;
		char *TAIL = str + len - 1;
		char temp;
		int i;
		for ( i = 0; i <= len / 2; i++, HEAD++, TAIL--) {
			temp = *HEAD;
			*HEAD = *TAIL;
			*TAIL = temp;
		}
   }
   char *main(char* theString)
   {
      rev(theString);
      return theString;
   }
End DynC


DYNASM RevStr(BYVAL s AS STRING) AS STRING
   // get length of string
   // divide by two
   // setup pointers to head and tail
   // iterate from 1 to (length \ 2)
   //   swap head with tail
   //   increment head pointer
   //   decrement tail pointer

   ENTER 0, 0 // = PUSH EBP: MOV EBP, ESP
   PUSH EBX // by Windows convention EBX, EDI, ESI must be saved before modification
   
   MOV EAX, s // get string pointer
   MOV ECX, EAX // duplicate it
   
   .WHILE BYTE PTR [ECX] <> 0

	INC ECX // propagate to tail 

   .WEND
   
   MOV EDX, ECX // duplicate tail pointer
   DEC EDX // set it to last byte before trailing zero
   
   SUB ECX, EAX // get length in ECX in 1 CPU cycle
   SHR ECX, 1 // get length \ 2 in 1 CPU cycle; that's the beauty of power-of-two division

   .WHILE ECX > 0
      
      MOV BL, [EDX] // no need to XOR; just overwrite BL and BH contents
      MOV BH, [EAX] // DynAsm deduces data size from destination register sizes
      
      MOV [EDX], BH // ditto, source register sizes
      MOV [EAX], BL
      
      INC EAX // propagate pointers
      DEC EDX
      
      DEC ECX // decrement counter
      
   .WEND
   
   // point to start of string again
   MOV EAX, s // MOV = 1 CPU cycle, PUSH + POP = 2 CPU cycles
   
   POP EBX // by Windows convention ESI, EDI, EBX must be restored if modified
   LEAVE // = POP EBP
   RET
END DYNASM