fgets problems Post: 302397047

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Top Forums Programming fgets problems Post 302397047 by CRGreathouse on Saturday 20th of February 2010 02:29:33 PM

02-20-2010

Registered User

Quote:

Originally Posted by Corona688

Memory is memory. It doesn't have to track the contents of the pari block to notice clobbering happening outside it.

Sure -- but that's not the problem (and it won't be the problem). Every time the library uses the stack it ensures that there's room for what it's creating. Also, the stack is very large -- at least 20 MB and sometimes as big as 1 GB, with its pointer avma moving by [only] several bytes per call.

The real problem with memory management is leaving garbage on the stack (another possibility is returning corrupted objects). The usual technique for is

Code:

GEN genericfunction(----) {
	pari_sp ltop = avma;	// Keep a pointer to the top of the stack's current location
	GEN r;	// Return value (assigned below)

	// ...
	
	r = gerepileupto(ltop, r);	// copy r to the top of the stack and move avma just above it
	return r;
}

which ensures that you're not leaving garbage on the stack. But this is somewhat more complicated by returning complicated objects like vectors. For example:

Code:

GEN vector = cgetg(4, t_VEC); // Make a vector
gel(vector, 1) = gen_2;
int i = 2;
for(; i < 4; i++)
  gel(vector, i) = addii(gel(vector, i-1), mulii(gel(vector, i-1), gel(vector, i-1))); // v[i] = v[i-1] + v[i-1]^2

Memory diagram:

(vector with pointers to its members A, B, and C)(A)(garbage)(B)(garbage)(C)

CRGreathouse

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LEARN ABOUT CENTOS

i2c_register_board_info

I2C_REGISTER_BOARD_I(9) 				      I2C and SMBus Subsystem					   I2C_REGISTER_BOARD_I(9)

NAME

       i2c_register_board_info - statically declare I2C devices

SYNOPSIS

       int i2c_register_board_info(int busnum, struct i2c_board_info const * info, unsigned len);

ARGUMENTS

       busnum
	   identifies the bus to which these devices belong

       info
	   vector of i2c device descriptors

       len
	   how many descriptors in the vector; may be zero to reserve the specified bus number.

DESCRIPTION

       Systems using the Linux I2C driver stack can declare tables of board info while they initialize. This should be done in board-specific init
       code near arch_initcall time, or equivalent, before any I2C adapter driver is registered. For example, mainboard init code could define
       several devices, as could the init code for each daughtercard in a board stack.

       The I2C devices will be created later, after the adapter for the relevant bus has been registered. After that moment, standard driver model
       tools are used to bind "new style" I2C drivers to the devices. The bus number for any device declared using this routine is not available
       for dynamic allocation.

       The board info passed can safely be __initdata, but be careful of embedded pointers (for platform_data, functions, etc) since that won't be
       copied.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014						   I2C_REGISTER_BOARD_I(9)

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