SEED equ 1234h
mov eax,SEED
mov ebx,not SEED
rol eax,3
ror ebx,13
add eax,ebx
adc eax,0
    

.data
SEED dd 1a8b3f57h ;;this will change/ be updated with every call rnd8

.code
;;example calling
RDTSC ;;read the clock timer on the CPU
mov [SEED],eax ;;set a new seed
call rnd8
cinvoke printf, "1 Random 8bits: %X", eax
call rnd8
cinvoke printf, "2 Random 8bits: %X", eax
call rnd8
cinvoke printf, "3 Random 8bits: %X", eax

;;function
rnd8:
MOV eax,[SEED]
MOV ecx,eax ;;copy
SHL eax,1 ;;shift out top bit
ADC ecx,71ae00h ;;add the carry bit and a constant
;;the constant repairs the zero seed = zero output case (hopefully)
SHL ecx,7 ;;shift out top 7 bits (7 is a PRIME number)
SHR eax,11 ;;shift out bottom 11 bits (11 is a PRIME number)
XOR eax,ecx ;;scramble the bits further using exclusive OR
BSWAP eax ;;reverse the byte order to extend the period 
;;(PERIOD: number of calls before the random sequence repeats itself)
MOV [SEED],eax ;;use this as the next iteration of the seed, ie seed.2
AND eax,0FFh ;;mask just the last 8bits 1byte
RET 0
    

.data 
SEED dd 1a8b3f57h ;;this will change/ be updated with every call rnd8 
.code 
;;example calling 
call GetTickCount 
call rnd8 
cinvoke printf, "1 Random 8bits: %X", eax 
call rnd8 
cinvoke printf, "2 Random 8bits: %X", eax 
call rnd8 
cinvoke printf, "3 Random 8bits: %X", eax 

;;function 
rnd8: 
MOV eax,[SEED] 
ADD ecx,eax ;;add eax to the unknown ecx state! randow like 
ROR eax,5 ;;rotate 5, it's still a pseudo random 
XOR eax,ecx ;;xor , increase randomness 
BSWAP eax ;;reverse the byte order to extend the period  
MOV [SEED],eax ;;use this as the next iteration of the seed, ie seed.2 
AND eax,0FFh ;;mask just the last 8bits 1byte 
RET 
    

erf.
this is wasty.

Code:

;;function 
rnd8: 
MOV eax,[SEED] 
ADD ecx,eax ;;add eax to the unknown ecx state! randow like 
...
    

this is better!

PS: or a generator that outputs 32bit on an 8bit range, that'd be as cool. Point is, I need to be able to reproduce the results exactly by seed at the end...

SEED dd 1

imul eax,[SEED],101b
bswap eax
rcr eax,3
sbb [SEED],eax    

Your ECX assumption Does Not Compute.

are you using gettickcount as your random source? why not rdtsc in that case?, I need speed and good distribution yet I must be able to reproduce the same output via seed, it's for an experiment I'm conducting.

random1:
rdtsc
add eax,edx
ror eax,7
xor eax,edx
ret

random2:
mov eax,[seedl]
mov edx,[seedh]
add ebx,eax
add ecx,edx
ror eax,19
xor eax,ecx
add eax,edx
sub eax,ebx
ret

random3:
mov eax,[eax]
mov eax,[eax]
mov eax,[eax]
mov eax,[eax]
mov eax,[eax]
ret