From: don on 27 Jun 2010 16:45 What are the rules for determining the number of times that a loop will occur given x and say you want to test for x < y or x > y or x = y or x <> y Where x would either start with 0 or 1 and you are going to be incrementing x by 1 inside the loop either before the test or after the test..... In otherwords, I"m trying to figure out how to determine the number of times that a loop would occcur based on the code.... I hope I"m making myself clear...... From: Rod Pemberton on 27 Jun 2010 21:29 "don" wrote in message news:i08da4\$8vd\$1(a)reader1.panix.com...> What are the rules for determining the number of times that a loop will > occur given x and say you want > to test for x < y or x > y or x = y or x <> y > Where x would either start with 0 or 1 and you are going to be > incrementing x by 1 inside the loop either before the test or after the > test..... > I'm not going attempt signed values. I'm assuming y is constant. For unsigned values, you usually use xy is used for decrementing x down to y+1. You've stated you want to increment x by 1 from 0 or 1, i.e., upto y, not decrement x. So, should we consider x>y? For unsigned values, if x starts with 0 and 1, x is incremented, x>y will be always be false unless x=1, y=0. I.e., it won't loop - except for x=1, y=0 which will loop forever. x>y should used for decrementing, not incrementing. I.e., x needs a starting value above y. y should be the low or ending value, e.g., 0 or 1. For unsigned values, x=y will only loop once, when x=y, but only if x=y initially for the first (and only) loop. That's the only time the comparison is true. So, I don't think we should consider x=y either. With one exception, for unsigned values, x<>y is effectively the same as xy, if x starts above y, x is decremented, should be similar... > incrementing ... before the test or after the test..... "inc... before the test", to me, indicates the test is at the start of the loop "inc... after the test", to me, indicates the test is at the end of the loop The difference is that one tests upon entry to the loop, whereas the other skips this initial test. I.e., a test at the end of the loop, allows the loop to execute at least once. Because of the loop, the non-initial loop tests occur in the same effective sequence. > In otherwords, I"m trying to figure out how to determine the number of times> that a loop would occcur based on the code.... I hope I"m making myself > clear...... > You need to work it through. Make sure you know where the test is to determine if the loop executes once automatically. Check the condition. Check what happens to some values with that condition. Check what happens at the boundaries, i.e., start values and ending values, with that condition, so you don't end up with off-by-one errors. Rod Pemberton From: wolfgang kern on 28 Jun 2010 04:44 "don" asked: > What are the rules for determining the number of times that a loop will > occur given x and say you want > to test for x < y or x > y or x = y or x <> y > Where x would either start with 0 or 1 and you are going to be > incrementing x by 1 inside the loop either before the test or after the > test..... > In otherwords, I"m trying to figure out how to determine the number of > times that a loop would occcur based on the code.... I hope I"m making > myself clear...... Loops can terminate on several conditions and may use any register or even variables in memory for the loop-count. ie:(ecx=iterations); MOV ecx,20h L0: code.. ;performs 32 times LOOP L0 ;does: dec ecx |jnz L0 ;but w/o flags altered but ie: MOV ecx,20h L0: code.. ;runs min.1 to max.32 times LOOPZ L0 ;loop terminates if 'code' produces 'NZ' ie:(bl=iteration-1);imply zero MOV ebx,400005h L0: code.. ;ie: MOV byte[ebx],20h ;implies [400000h] DEC bl JNS L0 ;BL=FFh after this ie:(ranged loops); MOV dx,1000 ; L0: code.. ; INC dx CMP dx,1400 ; JC L0 ;400 iterations ;JS L0 ;400 ;JNZ L0 ;400 ;JBE L0 ;401 An often seen confusion on x86 CPUs is that we got two variants for a zero in the counter register: LOOP with a zero in (e|r)cx will run 2**(16|32|64) times REP with a zero in (e|r)cx skips the string-instruction but both iterate (e|r)cx-times if nonzero. __ wolfgang  |  Pages: 1 Prev: the general server is not sufficientNext: BP disaster