i.5 6 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
Sent from my Verizon, Samsung Galaxy Tablet -------- Original message -------- From: Linda Alvord <[email protected]> Date: 7/29/19 1:10 PM (GMT-05:00) To: [email protected] Subject: Re: [Jprogramming] A bit-twisting puzzle I sent two mangled messages earlier. Here's what I can explain. I installed J on a samsungtablet and it seemed to be working. However PASTE removes some spaces. Package Manager is unable to print the page correctly so it can't be used. JVERSION Engine: j807/j32/android Release-d: commercial/2019-03-24T11:20:47 Library: 8.07.26 J Android: 1.2.06/27 Platform: Android 32 (armeabi-v7a) Installer: unknown InstallPath: /storage/emulated/0/Android/data/com.jsoftware.j.android/files Contact: https://nam04.safelinks.protection.outlook.com/?url=www.jsoftware.com&data=02%7C01%7C%7C75146b83bcac401ec0d008d71447a76e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637000170292186440&sdata=XWOHREdr7DU%2B6FzB3X37auSC8InadOXTKN%2BHurSRDks%3D&reserved=0 ]a=:i.3 4 0 1 2 3 4 5 6 7 I pasted this into my laptop to send it. Linda -----Original Message----- From: Programming <[email protected]> On Behalf Of Don Guinn Sent: Monday, July 29, 2019 11:04 AM To: Programming forum <[email protected]> Subject: Re: [Jprogramming] A bit-twisting puzzle Yes. IBM's going ahead and executing both legs of the conditional branch has always bothered me too. But I guess math units were relatively cheap and it presented a novel way to speed up conditional branches. Shades of quantum computing. My comment about destroying a was that a was not copied, but ored into a. On Mon, Jul 29, 2019 at 6:42 AM Henry Rich <[email protected]> wrote: > That's a good solution, same idea as Gilles's. As for OR destroying a > register, nowadays all registers are virtual anyway. Intel machines > have 150-odd registers in the execution unit IIRC, even though the > programming model presents only 16 to the programmer. Copying a > register doesn't even take an execution cycle - you just get a virtual > copy of the value you want. > > Yes, I am thinking Intel (if(!(a&&b)) appears 250 times in the JE). > Intel/AMD do not try executing both paths. I think their reasoning is > correct: since the branch predictor usually gets it right, it is > better to put all the processing power on the likely branch rather > than being guaranteed of having to discard half the work. > > Henry Rich > > On 7/29/2019 8:31 AM, Don Guinn wrote: > > First. Since you referred to BXLE I assume you are talking IBM 370 > > or beyond architecture. Unfortunately, I don't know INTEL > > instructions, but your example implies that maybe you are thinking INTEL. > > > > I have a problem with your use of "or" as wouldn't that destroy the > > contents of a? And several people have posted interesting responses > > there seem to be several good solutions. However, below is a > > solution for IBM > 360. > > > > L 2,A > > M 2,B RESULT IN REGISTER PAIR > > OR 2,3 TO SET CC AS M DOES NOT SET IT > > BNZ AROUND > > ... code > > AROUND EQU * > > > > > > A comment about branch taking a long time. Somewhere in the 1980's > > the > IBM > > 360 series of machines, whatever it's name was, performed an > > interesting bit of optimization for conditional branch. When a > > conditional branch > began > > execution both the fall-through and the target of the branch began > > execution. Seems there were two arithmetic units. Once the branch > > determined which path the branch should take, that path of execution > > was used and the other was discarded. Consequently, even though the > > branch itself took a long time it was completely overlapped with the > > instruction execution following the branch. The branch took no time > > as long as no > other > > conditional branch was encountered. > > > > On Sun, Jul 28, 2019 at 6:51 PM Henry Rich <[email protected]> wrote: > > > >> Many of the members of this Forum will remember the days of > >> assembler language > >> > >> ...and who could less than merry be > >> when writing out BXLE? > >> > >> AND, OR, XOR were our meat. Those days are returning. > >> > >> You have two integer variables a and b and you want to do something > >> if one or both of them are 0. In C, you might write > >> > >> if(a==0 || b==0)stmt; > >> > >> but that will generate the code > >> > >> cmp a,0 > >> bz stmt > >> cmp b,0 > >> bnz notstmt > >> stmt: > >> ... > >> notstmt: > >> > >> Here's the problem: your machine is very slow at branch instructions. > >> Each branch takes 30 times as long as a regular instruction. (I am > >> describing a state-of-the-art Intel CPU when it cannot predict the > >> branches effectively, perhaps because the data is... unpredictable). > >> > >> Obviously, you want to use only one branch instruction. You may > >> use as many arithmetic and logic instructions as you like, but only > >> one branch. The usual condition codes, ZNCV, are available. How > >> tight can you make the code? > >> > >> Example: suppose the problem were to execute stmt if one or both of > >> a and b is NOT zero. Then you would simply write > >> > >> or a,b > >> bnz notstmt > >> ... > >> > >> Checking for zero seems to be harder. > >> > >> No hurry. I have pondered this problem for over a year, and just > >> today I found a solution I consider acceptable. > >> > >> Henry Rich > >> > >> > >> > >> > >> > >> > >> > >> --- > >> This email has been checked for viruses by AVG. > >> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fw&data=02%7C01%7C%7C75146b83bcac401ec0d008d71447a76e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637000170292186440&sdata=yVB8gf7mGt3D%2By9k8El7adf0Fv9P8MXbv3kd4qeKFrk%3D&reserved=0 > >> ww.avg.com&data=02%7C01%7C%7Cd3a7362129bd413d41fd08d714360f4a%7 > >> C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637000094722556127& > >> sdata=pKfPBL%2F%2FCzAvcWzrgCTgUFdK%2FZEZOlIP9RHHBZEtw3s%3D&rese > >> rved=0 > >> > >> ------------------------------------------------------------------- > >> --- For information about J forums see > >> https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fww&data=02%7C01%7C%7C75146b83bcac401ec0d008d71447a76e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637000170292186440&sdata=f8u%2FgMK2iPjwpPng4ATq8vEJqGiCrUXraHprFj9BKvs%3D&reserved=0 > >> w.jsoftware.com%2Fforums.htm&data=02%7C01%7C%7Cd3a7362129bd413d > >> 41fd08d714360f4a%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C63700 > >> 0094722556127&sdata=La%2BQJlf0O0FX%2B5yZ4tCq2dB7h%2BcuF1ooN46qx > >> 8Jdga0%3D&reserved=0 > >> > > -------------------------------------------------------------------- > > -- For information about J forums see > > https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww&data=02%7C01%7C%7C75146b83bcac401ec0d008d71447a76e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637000170292196426&sdata=m2AZLq5ux9HL7ehBFXj5DzOqV%2FaoCElKCRV3RMZrGPM%3D&reserved=0 > > .jsoftware.com%2Fforums.htm&data=02%7C01%7C%7Cd3a7362129bd413d41 > > fd08d714360f4a%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C63700009 > > 4722556127&sdata=La%2BQJlf0O0FX%2B5yZ4tCq2dB7h%2BcuF1ooN46qx8Jdg > > a0%3D&reserved=0 > > ---------------------------------------------------------------------- > For information about J forums see > https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.j&data=02%7C01%7C%7C75146b83bcac401ec0d008d71447a76e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637000170292196426&sdata=g%2BFF1jDD7gWJzvYTbHWk8D78XkZ343vwyE8P4onUmyI%3D&reserved=0 > software.com%2Fforums.htm&data=02%7C01%7C%7Cd3a7362129bd413d41fd08 > d714360f4a%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C63700009472255 > 6127&sdata=La%2BQJlf0O0FX%2B5yZ4tCq2dB7h%2BcuF1ooN46qx8Jdga0%3D&am > p;reserved=0 > ---------------------------------------------------------------------- For information about J forums see https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.jsoftware.com%2Fforums.htm&data=02%7C01%7C%7C75146b83bcac401ec0d008d71447a76e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637000170292196426&sdata=DuSyXQcJWFMjmVikLVc1N%2BI9nVLQr8DA7EXs0afycv0%3D&reserved=0 ---------------------------------------------------------------------- For information about J forums see https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.jsoftware.com%2Fforums.htm&data=02%7C01%7C%7C75146b83bcac401ec0d008d71447a76e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637000170292196426&sdata=DuSyXQcJWFMjmVikLVc1N%2BI9nVLQr8DA7EXs0afycv0%3D&reserved=0 ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
