DISASM.dll is Win32 DLL to provide disassembler of byte code sequence. It supports 16 and 32 bit instructions up to Pentium 3 processor, including float point. It is using the same code as embedded disassemblers of SocketSpy and XEdit utilities. Price of full version of disasm.dll is US$19.99.
Source code of disassembler in ANSI C costs US$149.99
ASPID - New disassembler/decompiler tool
It has 2 export functions:
void SetIntelMode(int b32Bits)
The function select decoding mode, when b32Bits = 1, it will be 32 bit mode, otherwise 16 bit mode. The function has no return value.
int disassembler(unsigned char * pbyBuffer,
                 unsigned long dwAddress,
                 char * lpDisasmStr,
                 int bReturnWithCodes,
                 int bReturnWithAddress);
The function provides conversion of binary byte code sequence to ASCII string of assembler instruction.

Parameters:
pbyBuffer – pointer to byte array of the instruction queue, the buffer should be with read/write access and its contents may be modified during interpretation, because of this, use only copy of original instruction array.
dwAddress - physical addess (IP register value) for current instruction
lpStr – pointer to the char array to accept disassembled string, array should be big enough for disassembled string, instruction codes, and address of one instruction (usually 128 should enough)
bReturnWithCodes – return with code byte
(when bReturnWithCodes = 1, lpStr contains instruction codes, for example CD 2E INT 2E, otherwise it contains only assembler mnemonics - INT 2E.
bReturnWithAddress - lpStr begins with hex value of
dwAddress, for example: 04000000 CD 2E INT 2E.

Return value:
number of decoded byte, for example if you input pbyBuffer contains the for following codes:
CD 2E 90 2E 8A 1E 9C 90 F8 C3 50 26 8B 07 A9 02
00 75 05 2E FF 06 94 90-2E 80 3C 00 34 00 2B 0B
lpStr will receive string:
CD 2E INT 2E (bReturnWithCodes = 1) return value will be equal 2 and index of pbyBuffer should be incremented by 2 for next execution of disassembler function.
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Test application screen shot

Example of code

Code

#include 
#include "dasmdll.h"  //disassember DLL template
void main()
{
   char szDisasmBuffer[256];
   unsigned long dwAddressStart;
   unsigned long dwAddressEnd;
   unsigned char * pbyCodeBuffer;
   int nIndex;
   printf("Disassembler Test Application\n\n");
   _asm
   {
      start: mov eax,offset start
             mov dword ptr dwAddressStart,eax
             mov eax,offset end
             mov dword ptr dwAddressEnd,eax
             jmp end
//additional assembler lines, not executable
             sidt [ebx]
             clc
             mov  al,byte ptr [eax]
             push ds
             pop  dx
             call [eax+esi]
             imul eax
             bt   ax,1
      end:   nop
   }
   SetIntelMode(1 /* TRUE*/);
   nIndex = dwAddressEnd - dwAddressStart;
   pbyCodeBuffer = (unsigned char  *)malloc(nIndex); memcpy(pbyCodeBuffer,(const void*)dwAddressStart,nIndex);
   nIndex =  0;
   while((dwAddressStart+nIndex)<dwAddressEnd)
   { 
      nIndex + = disassembler(&pbyCodeBuffer[nIndex],dwAddressStart  nIndex
             szDisasmBuffer 1, 1);
      printf("%s",szDisasmBuffer);
   }
   free(pbyCodeBuffer);
}
Screen Shot of previous example