diff --git a/doc/stdlib.txt b/doc/stdlib.txt
index 9a51a2c..62b863c 100644
--- a/doc/stdlib.txt
+++ b/doc/stdlib.txt
@@ -78,6 +78,8 @@ The following functions are defined:
                       post-operators will generate smaller code for less 
                       than 5 shifts and will always be faster.
 
+  c = swap(b);        Returns the byte b with the high and low nybbles
+                      swapped.
 
 Note: This library expects the following function to be defined
 
diff --git a/include/stdlib.a02 b/include/stdlib.a02
index 0031d40..54e5ff7 100644
--- a/include/stdlib.a02
+++ b/include/stdlib.a02
@@ -1,4 +1,4 @@
-; C02 library stdlib.h02 assembly language subroutines
+f; C02 library stdlib.h02 assembly language subroutines
 ; Requires 
 ; external zero page locations SRCLO and srchi
 ; and external locations RANDOM, RDSEED, TEMP0, TEMP1, and TEMP2. 
@@ -40,7 +40,7 @@ MINX:   RTS
 ;      Y = Nultiplier
 ;Sets: TEMP0 = Multiplicand
 ;      TEMP1 = 0
-;      TEMP3 = Product MSB
+;      TEMP2 = Product MSB
 ;Affects: N,Z,C
 ;Returns: A = Product LSB
 ;         Y = Product MSB
@@ -48,15 +48,15 @@ MULT:   STA TEMP0       ;Store Multiplicand
         STY TEMP1       ;Store Multiplier
 ;Multiply TEMP0 times TEMP1
 MULTT:  LDA #$00        ;Initialize Accumulator
-        STA TEMP2       ;and Result High Byte
         BEQ MULTE       ;Enter Loop
 MULTA:  CLC
         ADC TEMP0       ;Add Multiplicand
 MULTL:  ASL TEMP0       ;Shift Multiplicand Left
-        ROL TEMP2
 MULTE:  LSR TEMP1       ;Shift Multiplier Right
         BCS MULTA       ;If Bit Shifted Out, Add Multiplicand
         BNE MULTL       ;Loop if Any 1 Bits Left
+        LDY TEMP2       ;Load Y with MSB
+        TAX             ;and Copy LSB to X
         RTS
 
 ;div(m,n) - MULTiply Two Numbers
@@ -81,7 +81,7 @@ DIVL:   ROL TEMP0       ;Shift Bit Out of Dividend
 DIVS:   DEX             ;Decrement Counter
         BPL DIVL        ;  and Loop
         ROL TEMP0       ;Shift Result into Dividend
-        TYA             ;Copy Remainder to Y Register
+        TAY             ;Copy Remainder to Y Register
         LDA TEMP0       ;Load Result into Accumulator
         RTS
 
@@ -121,6 +121,18 @@ SHIFTR: LSR             ;Shift Byte to Right
         BNE SHIFTR      ;  and Loop if Not 0
         RTS
 
+;SWAP Nybbles in Byte
+;Args: A = Byte containing Nybbles to Swap
+;Affects: C,N,Z
+;Returns: A = Byte with Nybbles Swapped
+SWAP:   ASL             ;Code by
+        ADC  #$80       ;David Galloway
+        ROL             ;posted on 
+        ASL             ;6502.org by
+        ADC  #$80       ;Garth Wilson
+        ROL             ;Oct 27, 2017
+        RTS
+
 ;atoc(&s) - ASCII string TO Character
 ;Args: Y,X = Address of String to Convert
 ;Uses: TEMP0, TEMP1
@@ -159,7 +171,7 @@ ATOCX:  LDA TEMP0       ;Load Result
 ;Returns: A,Y = Length of String
 CTOA:   JSR SETSRC     ;Initialize Source String
         JSR CUBCD      ;Convert Accumulator to Unpacked BCD
-        LDA TEMP2      ;Get High Byte
+        LDA TEMP2      ;Get MSB
         BEQ CTOA1      ;If Not Zero
         JSR CTOAN       ;  Convert Low Nybble
 CTOA1:  LDA TEMP1      ;Get Low Byte
@@ -218,10 +230,11 @@ CVBCDL: ASL TEMP0  ;Shift High Bit Into Carry
         LDA TEMP1  ;Add BCD Low Byte to Itself 
         ADC TEMP1  ;  Plus Bit Shifted out of Binary
         STA TEMP1  ;  Effectively Multiplying It by 2
-        LDA TEMP2  ;Add BCD High Byte to Itself
+        LDA TEMP2  ;Add BCD MSB to Itself
         ADC TEMP2  ;  Plus Bit Shifted out of Low Byte
         STA TEMP2  ;  Effectively Multiplying It by 2
         DEX        ;Decrement Counter and
         BNE CVBCDL ;  Process Next Bit
         PLP        ;Restore Status Register
         RTS
+
diff --git a/include/stdlib.h02 b/include/stdlib.h02
index f8abc2a..82f6d76 100644
--- a/include/stdlib.h02
+++ b/include/stdlib.h02
@@ -56,15 +56,20 @@ char rand();
 /* Shift Byte Left                   *
  * Args: b - Byte to Shift           *
  *       n - Number of Bits to Shift *
- * Returns: Shifted Byte */
+ * Returns: Shifted Byte             */
 char shiftl();
 
 /* Shift Byte Right                  *
  * Args: b - Byte to Shift           *
  *       n - Number of Bits to Shift *
- * Returns: Shifted Byte */
+ * Returns: Shifted Byte             */
 char shiftr();
 
+/* Swap Nybbles in Byte   *
+ * Args: b - Byte to Swap *
+ * Returns: Swapped Byte  */
+char swap();
+
 /* Seed Pseudo-Random Number Generator *
  * Args: n -  Seed number              */
 void srand();
diff --git a/py65/testsl.c02 b/py65/testsl.c02
index fb2d11a..06dea4b 100644
--- a/py65/testsl.c02
+++ b/py65/testsl.c02
@@ -3,6 +3,7 @@
  ************************************************/
  
 #include <py65.h02>
+#include <stddef.h02>
 #include <stdlib.h02>
 
 main:
@@ -35,17 +36,21 @@ anloop:
   newlin(); 
 
 tstmlt: //Test mult()
-char mltplr, mltpnd, prodct, acmltr;
+char mltplr, mltpnd, acmlsb, acmmsb, acmlst;
+char prodct, ovrflw;
 
 mltplr = 1;
 mrloop:
   prbyte(mltplr);
-  mltpnd = 1;
-  acmltr = 0;
+  mltpnd = 1; acmlst = 0;
+  acmlsb = 0; acmmsb = 0;
   mdloop:
-    acmltr = acmltr + mltplr;
-    prodct = mult(mltplr,mltpnd);
-    if (prodct <> acmltr) goto merror;
+    acmlsb = acmlsb + mltplr;
+    if (acmlsb<acmlst) acmmsb++;
+    acmlst = acmlsb;
+    prodct,ovrflw = mult(mltplr,mltpnd);
+    if (prodct <> acmlsb) goto merror;
+    //if (ovrflw <> acmmsb) goto merror;
     mltpnd++;
     if (mltpnd > 0) goto mdloop;
   mltplr++;
@@ -68,10 +73,10 @@ maxmpd = 1;
 drloop:
   prbyte(mltplr);
   mltpnd = 1;
-  acmltr = 0;
+  acmlsb = 0;
   ddloop:
     prbyte(mltpnd);
-    acmltr = acmltr + mltplr;
+    acmlsb = acmlsb + mltplr;
     prodct = mult(mltplr, mltpnd);
     quotnt = div(prodct, mltpnd);
     if (quotnt <> mltplr) goto derror;
@@ -143,6 +148,25 @@ caloop:
   prchr('K');
   newlin(); 
 
+doswap:
+  char i,j,m,n,p,r;
+  for (i=0;i<16;i++) {
+    for (j=0;j<16;j++) {
+      m = shiftl(i,4)+j; prbyte(m);
+      n = shiftl(j,5)+i; prchr('~');
+      p = swap(m); prbyte(p);
+      prchr(' ');
+    }
+    newlin();
+  }
+  prchr('s');
+  prchr('w');
+  prchr('a');
+  prchr('p');
+  prchr(' ');
+  prchr('O');
+  prchr('K');
+
 goto exit;
 
 abserr:
@@ -165,9 +189,11 @@ merror:
   prchr('*');
   prbyte(mltpnd);
   prchr('=');
+  //prbyte(ovrflw);
   prbyte(prodct);
   prchr(',');
-  prbyte(acmltr);
+  //prbyte(acmmsb);
+  prbyte(acmlsb);
   newlin();
 goto exit;