the Exe should be ran under CONSOLE subsystem
the NEG is just plus one after the operand has been NOT,
cause its arithmetic instruction
i mean take WORD for example
10000 H- 0F??FH
What is your question?
neg(x) = (NOT x) + 1
e.g. WORD values
neg(1) = (0xfffe) + 1 = 0xffff = -1
neg(0xffff) = (0) + 1 = 1
generally speaking, NOT is regarded as a logical function, while NEG is a math function
that may seem like splitting hairs :P
but - the devil is in the details - in this case, the flags
NOT doesn't alter any flags, while NEG does - most notably, the sign, zero, and carry flags
that actually makes NOT unusual, even as a logical instruction
most logical instructions clear the carry flag and set the sign and zero flags according to results
i have had occassions where i wished it did set the flags, too :(
Hi,
NEG is twos complement negation, NOT is either
a ones complement negation or a logical bitwise AND.
Quote
NOT doesn't alter any flags, while NEG does - most notably, the sign, zero, and carry flags
that actually makes NOT unusual, even as a logical instruction
most logical instructions clear the carry flag and set the sign and zero flags according to results
i have had occassions where i wished it did set the flags, too
Yeah, odd. And note, that TEST is described as a
non-destructive AND, and it sets the flags. So you
could do a TEST - AND or an AND - TEST sequence
if needed. (Not that I ever remember to do that the
first time around...)
Regards,
Steve N.
Quote from: qWord on June 14, 2012, 06:53:20 PM
What is your question?
no questions at all, just make a little program to do some demonstration :biggrin:
although its simple, i think someone my need this
Hi,Dave,FORTRANS and qWord
for the two's complementation ,
if gives 0
then NEG(0)=[NOT(0)=FFFFFFFF] + 1 =0
also 100000000 - 0 = 100000000 or just 00000000
in MASM , we can use CARRY? to test whether CARRY FLAG is set
but in GoAsm, what should i use?
and for other Flags test,is there any OPCAODE?
there are branch instructions that branch or do not branch, based on the state of specific flags
if you NEG a value that was 0, it remains 0
the carry flag will be cleared and the zero flag will be set
for all other values, the carry flag will be set and the zero flag will be cleared
if you NEG a "max negative" value (80h for bytes, 8000h for words, or 80000000h for dwords)
the value remains unchanged and the overflow flag is set
for all other values, the overflow flag is cleared
the sign flag always reflects the sign of the result
you can use any of the conditional branch instructions following NEG
****************************************************************
Equality Branches (Used for Signed or Unsigned Comparisons)
----------------------------------------------------------------
Instruction Description Condition Aliases
----------------------------------------------------------------
JZ Jump if equal ZF=1 JE
JNZ Jump if not equal ZF=0 JNE
****************************************************************
****************************************************************
Unsigned Branches
----------------------------------------------------------------
Instruction Description Condition Aliases
----------------------------------------------------------------
JA Jump if above CF=0 and ZF=0 JNBE
JAE Jump if above or equal CF=0 JNC JNB
JB Jump if below CF=1 JC JNAE
JBE Jump if below or equal CF=1 or ZF=1 JNA
****************************************************************
****************************************************************
Signed Branches
----------------------------------------------------------------
Instruction Description Condition Aliases
----------------------------------------------------------------
JG Jump if greater SF=OF or ZF=0 JNLE
JGE Jump if greater or equal SF=OF JNL
JL Jump if less SF<>OF JNGE
JLE Jump if less or equal SF<>OF or ZF=1 JNG
JO Jump if overflow OF=1
JNO Jump if no overflow OF=0
JS Jump if sign SF=1
JNS Jump if no sign SF=1
****************************************************************
there are also JPO and JPE - parity
the parity flag is set if there are an even number of 1's in the low byte
the parity flag is cleared if there are an odd number of 1's in the low byte
the parity flag was used back in the days of serial communications, and is rarely used now