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PR: 2078

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Submitted by: Dale Anderson <dra@redevised.net>
Approved by: steve@openssl.org

Corrections to bn_internal documentation.
This commit is contained in:
Dr. Stephen Henson 2009-10-28 13:51:56 +00:00
parent 169bfde4d4
commit 67bcde9ba8
1 changed files with 19 additions and 9 deletions
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28
doc/crypto/bn_internal.pod
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@ -72,24 +72,34 @@ applications.
=head2 The BIGNUM structure
typedef struct bignum_st
typedef struct bignum_st BIGNUM;
struct bignum_st
{
int top; /* number of words used in d */
BN_ULONG *d; /* pointer to an array containing the integer value */
int max; /* size of the d array */
int neg; /* sign */
} BIGNUM;
BN_ULONG *d; /* Pointer to an array of 'BN_BITS2' bit chunks. */
int top; /* Index of last used d +1. */
/* The next are internal book keeping for bn_expand. */
int dmax; /* Size of the d array. */
int neg; /* one if the number is negative */
int flags;
};
The integer value is stored in B<d>, a malloc()ed array of words (B<BN_ULONG>),
least significant word first. A B<BN_ULONG> can be either 16, 32 or 64 bits
in size, depending on the 'number of bits' (B<BITS2>) specified in
C<openssl/bn.h>.
B<max> is the size of the B<d> array that has been allocated. B<top>
B<dmax> is the size of the B<d> array that has been allocated. B<top>
is the number of words being used, so for a value of 4, bn.d[0]=4 and
bn.top=1. B<neg> is 1 if the number is negative. When a B<BIGNUM> is
B<0>, the B<d> field can be B<NULL> and B<top> == B<0>.
B<flags> is a bit field of flags which are defined in C<openssl/bn.h>. The
flags begin with B<BN_FLG_>. The macros BN_set_flags(b,n) and
BN_get_flags(b,n) exist to enable or fetch flag(s) B<n> from B<BIGNUM>
structure B<b>.
Various routines in this library require the use of temporary
B<BIGNUM> variables during their execution. Since dynamic memory
allocation to create B<BIGNUM>s is rather expensive when used in
@ -209,12 +219,12 @@ significant non-zero word plus one when B<a> has shrunk.
=head2 Debugging
bn_check_top() verifies that C<((a)-E<gt>top E<gt>= 0 && (a)-E<gt>top
E<lt>= (a)-E<gt>max)>. A violation will cause the program to abort.
E<lt>= (a)-E<gt>dmax)>. A violation will cause the program to abort.
bn_print() prints B<a> to stderr. bn_dump() prints B<n> words at B<d>
(in reverse order, i.e. most significant word first) to stderr.
bn_set_max() makes B<a> a static number with a B<max> of its current size.
bn_set_max() makes B<a> a static number with a B<dmax> of its current size.
This is used by bn_set_low() and bn_set_high() to make B<r> a read-only
B<BIGNUM> that contains the B<n> low or high words of B<a>.