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From: slover on 2 Jan 2006 07:45
Hello,
I try to translate library written in Nasm to c-code, but I have
problem with this construction:

shmulti1:
xor eax, eax
lodsb

mul bl
movzx ecx, mult
add eax, DWORD PTR out_text_m_index[ecx*4]

push esi
mov esi, eax
rep movsb
pop esi

dec dx
jnz SHORT shmulti1

out_text_m_index and out_text_m_table is define such as:
out_text_m_index DD 00000h + OFFSET out_text_m_table
DD 00009h + OFFSET out_text_m_table
DD 00023h + OFFSET out_text_m_table

out_text_m_table DB 000h
DB 000h,000h,000h,000h
DB 01Fh,000h,000h,03Fh
DB 001h,0FFh,000h,00Ch

Can you help me with meaning?
Thank you
Pavel Slavik

From: randyhyde@earthlink.net on 2 Jan 2006 11:11
Are there no comments telling you what this code is supposed to be
doing?
Cheers,
Randy Hyde

slover wrote:
> Hello,
> I try to translate library written in Nasm to c-code, but I have
> problem with this construction:
>
> shmulti1:
> xor eax, eax
> lodsb
>
> mul bl
> movzx ecx, mult
> add eax, DWORD PTR out_text_m_index[ecx*4]
>
> push esi
> mov esi, eax
> rep movsb
> pop esi
>
> dec dx
> jnz SHORT shmulti1
>
> out_text_m_index and out_text_m_table is define such as:
> out_text_m_index DD 00000h + OFFSET out_text_m_table
> DD 00009h + OFFSET out_text_m_table
> DD 00023h + OFFSET out_text_m_table
>
> out_text_m_table DB 000h
> DB 000h,000h,000h,000h
> DB 01Fh,000h,000h,03Fh
> DB 001h,0FFh,000h,00Ch
>
> Can you help me with meaning?
> Thank you
> Pavel Slavik

From: Herbert Kleebauer on 2 Jan 2006 16:00
slover wrote:
> I try to translate library written in Nasm to c-code, but I have
> problem with this construction:

Doesn't make much sense. If ecx=0 is not allowed, then the first
entry in out_text_m_index is not used and therefore the first 9 bytes
in out_text_m_table are wasted. But if ecx=0 then "rep movsb" does
nothing, so again the first 9 bytes in out_text_m_table are wasted.

But a more interesting question for the NASM (or Intel syntax user):
How do you know what the instruction "movzx ecx, mult" does?
Is it a byte-to-long or a word-to-long move? What is "mult"? It can't
be a constant and if it is an address, why isn't there a [mult] or
BYTE PTR mult? Or is there somewhere in the source a line like
%define mult [ebp+8]
and without knowing this line you can't understand what "movzx ecx, mult"
does? And that really is called assembly programming?

> shmulti1:
> xor eax, eax
> lodsb
>
> mul bl
> movzx ecx, mult
> add eax, DWORD PTR out_text_m_index[ecx*4]
>
> push esi
> mov esi, eax
> rep movsb
> pop esi
>
> dec dx
> jnz SHORT shmulti1
>
> out_text_m_index and out_text_m_table is define such as:
> out_text_m_index DD 00000h + OFFSET out_text_m_table
> DD 00009h + OFFSET out_text_m_table
> DD 00023h + OFFSET out_text_m_table
>
> out_text_m_table DB 000h
> DB 000h,000h,000h,000h
> DB 01Fh,000h,000h,03Fh
> DB 001h,0FFh,000h,00Ch
From: greg.johnston on 2 Jan 2006 17:45
"mult d[x] [y]" must be somewhere else in the source, assuming usual
FASM/NASM-like behavior of the assembler. It looks like part of the
difficulty with this code is that it's not complete (lack of shmult1
label, for example).

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