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TheDuchy
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;
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; pker's Random Number Generator (PKRNG)
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; ======================================
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;
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;
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; Description
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; -----------
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;
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; PKRNG is a random number generator. It can be used for MASM, TASM, FASM, etc. It
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; containz four procedurez: __randomize, __random and __m_seq_gen and
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; __random_rdtsc. __randomize procedure is for generating initial seed in the seed
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; field, which specified as parameter. The __m_seq_gen procedure is used to
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; generate m-sequence, which used by __random, which generate random numberz
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; finally. __random_rdtsc is the simplest one, it just get the RDTSC and divide it
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; by the range given as parameter.
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;
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;
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; How to use PKRNG
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; ----------------
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;
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; When using MASM or TASM to initialize seed field:
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;
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; mov edi,offset dwSeed
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; call __randomize
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;
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; The get a random number in eax:
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;
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; mov eax,offset dwSeed
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; mov ecx,32 ; get a random number between 0~31
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; call __random
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;
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;
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; Same thing happened with FASM:
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;
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; mov edi,dwSeed
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; call __randomize
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;
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; mov eax,dwSeed
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; mov ecx,32 ; get a random number between 0~31
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; call __random
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;
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;
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; Copyright
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; ---------
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;
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; (c) 2004. No rightz reserved. Use without permission :P.
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;
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;
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; __randomize procedure
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; =====================
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;
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;
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; Description
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; -----------
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;
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; This function use RDTSC instruction to generator a random number in order to
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; initialize the seed field.
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;
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;
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; Parameterz and Return Values
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; ----------------------------
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;
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; input:
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; edi --- points to the seed field
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; output:
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; nothing
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;
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__randomize: pushad
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db 0fh,31h ; RDTSC
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add eax,edx ; ...
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stosd ; fill in the seed buffer
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popad
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ret
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;
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; __random procedure
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; ==================
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;
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;
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; Description
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; -----------
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;
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; This function generates a random number and rewrite the seed field. The function
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; first get a 32 bit m-sequence, which then multiply with the previous seed, with
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; __m_seq_gen procedure. And then, it calls __m_seq_gen again to generate another
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; m-sequence to make noise by adding on the DWORD calculated before. Also, this
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; result is the new seed, and will be write to the seed field which pointed by EAX
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; as argument. Finally, the seed is divided by ECX, and return the modulus, which
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; is the expected random number.
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;
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;
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; Parameterz and Return Values
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; ----------------------------
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;
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; input:
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; eax --- pointz to the random seed field
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; edx --- the range of the random number to be generated
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; output:
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; eax --- random number as result
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;
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__random: pushad
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xchg ecx,edx
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mov edi,eax
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mov esi,eax
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lodsd ; get the previous seed value
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mov ebx,eax
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mov ebp,ebx
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call __m_seq_gen ; generate a m-sequence
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imul ebp ; multiply with the previous seed
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xchg ebx,eax
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call __m_seq_gen ; generate anothe m-sequence
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add eax,ebx ; to make noise...
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add eax,92151fech ; and some noisez...
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stosd ; write new seed value
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xor edx,edx
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div ecx ; calculate the random number
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mov [esp+28],edx ; according to a specified range
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popad
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ret
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;
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; __m_seq_gen procedure
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; =====================
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;
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;
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; Description
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; -----------
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;
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; This function use a PN (Pseudo Noise) generator to generate m-sequencez. The
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; configuration of the generator shows below (figure 1):
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;
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; (module 2 addition)
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; ___
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; / \
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; +---------- | + | <------------------------------+
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; | \___/ |
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; | A |
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; | +-----+ | +-----+ +-----+ |
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; +--> | D31 | -+-> | D30 | ---> ... ---> | D01 | -+-> output
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; +-----+ +-----+ +-----+
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; A A A
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; | | |
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; CLK ---------------+------------+---------------------+
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;
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; figure 1. m-Sequence Generator
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;
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;
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; Parameterz and Return Values
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; ----------------------------
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;
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; input:
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; eax --- a non-zero random number, which could be generated by RDTSC or
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; GetTickCount or such functionz
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; output:
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; eax --- the result of the function
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;
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__m_seq_gen: pushad
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xor esi,esi ; use to save the 32bit m-sequence
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push 32 ; loop 32 times (but it's not a
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pop ecx ; cycle in the m-sequence generator)
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msg_next_bit: mov ebx,eax
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mov ebp,ebx
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xor edx,edx
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inc edx
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and ebp,edx ; get the lowest bit
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dec cl
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shl ebp,cl
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or esi,ebp ; output...
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inc cl
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and ebx,80000001h ; \
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ror bx,1 ; \
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mov edx,ebx ; \
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ror ebx,16 ; module 2 addition
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xor bx,dx ; /
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rcl ebx,17 ; /
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rcr eax,1 ; /
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loop msg_next_bit
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mov [esp+28],esi
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popad
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ret
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;
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; __random_rdtsc procedure
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; ========================
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;
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;
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; Description
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; -----------
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;
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; This is the simplest RNG in the packet. Well, nothing to explain :P
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;
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;
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; Parameterz and Return Value
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; ---------------------------
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;
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; input:
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; ecx --- the range of the random number to be generated
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;
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; output:
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; eax --- random number as result
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;
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__random_rdtsc: pushad
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db 0fh,31h
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add eax,edx
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xor edx,edx
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or ecx,ecx
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jz rnd_rdt_no_range
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div ecx
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xchg eax,edx
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rnd_rdt_no_range:
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mov [esp+28],eax
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popad
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ret
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