On Fri, 21 Feb 2014 05:55:02 -0000, Yousuf Khan
wrote:

On 20/02/2014 11:21 PM, Paul wrote:
At one time, a compiler would issue instructions
from about 30% of the instruction set. It would mean
a compiled program would never emit the other 70% of
them. But a person writing assembler code, would
have access to all of them, at least, as long as
the mnemonic existed in the assembler.

I think the original idea of the x86's large instruction count was to
make an assembly language as full-featured as a high-level language. x86
even had string-handling instructions!

I remember I designed an early version of the CPUID program that ran
under DOS. The whole executable including its *.exe headers was
something like 40 bytes! Got it down to under 20 bytes when I converted
it to *.com (which had no headers)! Most of the space was used to store
strings, like "This processor is a:" followed by generated strings like
386SX or 486DX, etc.

You could make some really tiny assembler programs on x86. Of course,
compiled programs ignored most of these useful high-level instructions
and stuck with simple instructions to do everything.

Yousuf Khan
Did you cater for all the early cpus?

;This code assembles under nasm as 105 bytes of machine code, and will
;return the following values in ax:
;
;AX CPU
;0 8088 (NMOS)
;1 8086 (NMOS)
;2 8088 (CMOS)
;3 8086 (CMOS)
;4 NEC V20
;5 NEC V30
;6 80188
;7 80186
;8 286
;0Ah 386 and higher

code segment
assume cs:code,ds:code
..radix 16
org 100

mov ax,1
mov cx,32
shl ax,cl
jnz x186

;pusha
db '60'
stc
jc nec

mov ax,cs
add ax,01000h
mov es,ax
xor si,si
mov di,100h
mov cx,08000h
;rep es movsb
rep es:movsb
or cx,cx
jz cmos
nmos:
mov ax,0
jmp x8_16
cmos:
mov ax,2
jmp x8_16
nec:
mov ax,4
jmp x8_16
x186:
push sp
pop ax
cmp ax,sp
jz x286

mov ax,6
x8_16:
xor bx,bx
mov byte [a1],043h
a1 label byte
nop
or bx,bx
jnz t1
or bx,1
t1:
jmp cpuid_end
x286:
pushf
pop ax
or ah,070h
push ax
popf
pushf
pop ax
and ax,07000h
jnz x386

mov ax,8
jmp cpuid_end
x386:
mov ax,0Ah

cpuid_end:


code ends

end


--
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