help with data type sizes Post: 302488038

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Top Forums Programming help with data type sizes Post 302488038 by DGPickett on Friday 14th of January 2011 04:44:54 PM

01-14-2011

Registered User

When loading phydsical accumulators and registers with numbers, they are stretched to fit, with zeros if unsigned or by repeating the sign bit at the high order bit of the comp-2 representation. Similarly, C stretches the values to the bigger type to compare or compute.

Usually, a char is 1 byte unsigned (0-255), and an int is 4 bytes signed (+/- 2 billion plus). Old C models had int and short at 2 and long at 4, most 32 bit models have int and long at 4, and long models have int at 4 and long at 8.

Floating types are particularly variable in computers, but in C it is 4 bytes, and there is an IEEE spec on floating numbers that makes them portable. Differnt float types are 64 Double or 80 Long Double or is it Double Double, no, that feels wrong, bits. Float has some bits for mantissa, usually as a 2's complement fraction between .5 and < 1.0 when normalized, where 010000- is 1/2, and exponent, usually a 2's complement power of 2 but sometimes a 2's complement power of 16 or an "excess" number, where the boundary between negative and positive is shifted to a more useful range. None of this leaks into IEEE floating representations.

C increments pointers for each type by its size. types.h gives a lot of info on alternative C types. Some APIs just typedef their int types int1, int2, int4 and int8 or unsigned uint1, uint2, uint4, uint8.

Positions of items in a struct are usualy formatted #pragma pack 4 by default, and generally, you can save space by declaring like sized types adjacent.

Last edited by DGPickett; 01-14-2011 at 05:57 PM..

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LEARN ABOUT DEBIAN

xgsch2pcb

xgsch2pcb(1)															      xgsch2pcb(1)

NAME

       xgsch2pcb - gEDA/gaf gschem -> PCB workflow GUI

SYNOPSIS

       xgsch2pcb [project]

DESCRIPTION

       When  designing	a printed circuit board (PCB) it's often desirable to create a 'schematic' which shows the components to be used and their
       connectivity in an abstract fashion.  The connectivity information is then used to help when designing the actual circuit board.

       gsch2pcb is a command-line tool, part of the gEDA suite, which is used to generate and update a PCB layout.  It works with schematics  cre-
       ated by gschem, part of the gEDA suite, and layouts created by pcb, a PCB layout system commonly used with gEDA.

       xgsch2pcb provides an intuitive, user-friendly graphical interface to gsch2pcb.

       The main window is divided into three main areas:

       o  The toolbar at the top offers the usual options to quit the program and to load and save project files.

       o  The  left  hand  'Schematic'	frame shows a list of schematic pages that the PCB layout will be based on. The 'Edit schematic' and 'Edit
	  attributes' buttons respectively launch gschem and gattrib to edit the selected schematic page.

       o  The right hand 'Layout' pane shows the name of the PCB layout file associated with the project. The 'Edit layout' button launches pcb to
	  edit	a  file, and will offer to update your PCB layout if necessary. The 'Update layout' button forces an update of the PCB layout even
	  if one isn't strictly necessary.

       The update process will carry out the following actions to modify your layout, after launching pcb if isn't already running:

       1.  Remove any elements from the layout that are not in the schematic.

       2.  Find any elements that are in the schematic but not in the layout, and add them to the layout (in the top left corner). N.b. that  it's
	   probably a good idea to leave this corner of your layout clear until the layout is more or less finalised, to avoid new elements inter-
	   fering with elements which have already been placed and routed.

       3.  Clear your rats and load a new rats nest.

       4.  Update the component pin names to match the pin names on the schematic symbol.

       Note that the update process won't modify your PCB file on disk, and will take into account any changes you have made since you last saved.

								  02 January 2010						      xgsch2pcb(1)

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