assembly - General Purpose Registers - Order -

-

why general purpose registers ordered (eax, ecx, edx, ebx)? example, "inc" instruction opcodes are:

inc eax - 40 inc ecx - 41 inc edx - 42 inc ebx - 43

is there reason why ordered way?

the odd placement of (e)bx due way 8086 evolved 8080.

the 8080 has accumulator (a) , 6 general-purpose registers b, c, d, e, h , l, b/c, d/e , h/l can used in pairs, , in particular h/l can used address memory access. 8086 designed existing 8080 code translated it; guess seemed logical map registers in following order:

8080 register   -> 8086 internal register 0               b,c ->                        1               d,e ->                        2               h,l ->                        3               sp  ->                        4

as noted in answer, ax, bx, cx , dx in 8086 not arbitrary names 4 general-purpose registers - have mnemonic meanings special functions registers have: "accumulator", "base", "count" , "data". given above mapping, makes sense assign "accumulator" function internal register 0, , "base" function internal register 3. (and 8086 internal registers 5, 6 , 7 bp, si , di, new functionality.)

of course, informed (see here example) speculation - 8086 designers know sure...


Comments

Post a Comment

Popular posts from this blog

C#: Application without a window or taskbar item (background app) that can still use Console.WriteLine() -

-
i'm trying create application adheres following: no taskbar no console or form window can utilize console.writeline() . (i.e. if executes app command prompt write console.) the problem if create windows form (or wpf) application can have there no taskbar, console or window show up, console.writeline() nothing. if create console app, writes console, can't figure out how hide (and if did hide it, write command prompt window?)... how do this? just create standard console application. callers responsibility hide window caused program (from how run c# console application console hidden ): system.diagnostics.processstartinfo start = new system.diagnostics.processstartinfo(); start.filename = dir + @"\myprocesstostart.exe"; start.windowstyle = system.diagnostics.processwindowstyle.hidden;
Read more

c++ - Convert big endian to little endian when reading from a binary file -

-
this question has answer here: how convert between big-endian , little-endian values in c++? 28 answers i've been looking around how convert big-endian little-endians. didn't find solve problem. seem there's many way can conversion. anyway following code works ok in big-endian system. how should write conversion function work on little-endian system well? this homework, since systems @ school running big-endian system. it's got curious , wanted make work on home computer also #include <iostream> #include <fstream> using namespace std; int main() { ifstream file; file.open("file.bin", ios::in | ios::binary); if(!file) cerr << "not able read" << endl; else { cout << "opened" << endl; int i_var; double d_var; while(!file.eof()) {...
Read more

openssl - Load PKCS#8 binary key into Ruby -

-
i'm trying load particular private key encoded in binary der format ( pkcs#8 ) ruby. however, openssl::pkey won't recognize it. can make work doing console work , transforming pem so: openssl pkcs8 -inform der -in file.key -passin pass:xxxxxxxx >private_key.pem after this, key can correctly read. however, since whole process done in memory instead of writing , reading files. so question is: possible load private keys binary encoded der format ruby/openssl? thank time, fernando yes, can indirectly load pkcs#8 der-encoded private keys using ruby openssl. openssl::pkey::rsa.new handle pem-formatted pkcs#8, easy read binary der , convert pem-formatted string , load string. for example, these der-encoded private keys: $ openssl genrsa | openssl pkcs8 -topk8 -outform der \ -nocrypt -out pkcs8.key $ openssl genrsa | openssl pkcs8 -topk8 -outform der \ -v2 des3 -passout pass:secret -out pkcs8_des3.key you can this: require 'open...
Read more