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MP(2)                         System Calls Manual                        MP(2)



NAME
       mpsetminbits,  mpnew, mpfree, mpbits, mpnorm, mpcopy, mpassign, mprand,
       strtomp, mpfmt,mptoa, betomp, mptobe, letomp, mptole,  mptoui,  uitomp,
       mptoi,  itomp,  uvtomp,  mptouv,  vtomp, mptov, mpdigdiv, mpadd, mpsub,
       mpleft, mpright, mpmul,  mpexp,  mpmod,  mpdiv,  mpcmp,  mpextendedgcd,
       mpinvert,   mpsignif,   mplowbits0,   mpvecdigmuladd,   mpvecdigmulsub,
       mpvecadd, mpvecsub, mpveccmp, mpvecmul, mpmagcmp,  mpmagadd,  mpmagsub,
       crtpre,  crtin,  crtout,  crtprefree,  crtresfree  - extended precision
       arithmetic

SYNOPSIS
       #include <u.h>
       #include <libc.h>
       #include <mp.h>

       mpint*  mpnew(int n)

       void    mpfree(mpint *b)

       void    mpsetminbits(int n)

       void    mpbits(mpint *b, int n)

       void    mpnorm(mpint *b)

       mpint*  mpcopy(mpint *b)

       void    mpassign(mpint *old, mpint *new)

       mpint*  mprand(int bits, void (*gen)(uchar*, int), mpint *b)

       mpint*  strtomp(char *buf, char **rptr, int base, mpint *b)

       char*   mptoa(mpint *b, int base, char *buf, int blen)

       int     mpfmt(Fmt*)

       mpint*  betomp(uchar *buf, uint blen, mpint *b)

       int     mptobe(mpint *b, uchar *buf, uint blen, uchar **bufp)

       mpint*  letomp(uchar *buf, uint blen, mpint *b)

       int     mptole(mpint *b, uchar *buf, uint blen, uchar **bufp)

       uint    mptoui(mpint*)

       mpint*  uitomp(uint, mpint*)

       int     mptoi(mpint*)

       mpint*  itomp(int, mpint*)

       mpint*  vtomp(vlong, mpint*)

       vlong   mptov(mpint*)

       mpint*  uvtomp(uvlong, mpint*)

       uvlong  mptouv(mpint*)

       void    mpadd(mpint *b1, mpint *b2, mpint *sum)

       void    mpmagadd(mpint *b1, mpint *b2, mpint *sum)

       void    mpsub(mpint *b1, mpint *b2, mpint *diff)

       void    mpmagsub(mpint *b1, mpint *b2, mpint *diff)

       void    mpleft(mpint *b, int shift, mpint *res)

       void    mpright(mpint *b, int shift, mpint *res)

       void    mpmul(mpint *b1, mpint *b2, mpint *prod)

       void    mpexp(mpint *b, mpint *e, mpint *m, mpint *res)

       void    mpmod(mpint *b, mpint *m, mpint *remainder)

       void    mpdiv(mpint *dividend, mpint *divisor,  mpint *quotient,
               mpint *remainder)

       int     mpcmp(mpint *b1, mpint *b2)

       int     mpmagcmp(mpint *b1, mpint *b2)

       void    mpextendedgcd(mpint *a, mpint *b, mpint *d, mpint *x,
               mpint *y)

       void    mpinvert(mpint *b, mpint *m, mpint *res)

       int     mpsignif(mpint *b)

       int     mplowbits0(mpint *b)

       void    mpdigdiv(mpdigit *dividend, mpdigit divisor,
               mpdigit *quotient)

       void    mpvecadd(mpdigit *a, int alen, mpdigit *b, int blen,
               mpdigit *sum)

       void    mpvecsub(mpdigit *a, int alen, mpdigit *b, int blen,
               mpdigit *diff)

       void    mpvecdigmuladd(mpdigit *b, int n, mpdigit m, mpdigit *p)

       int     mpvecdigmulsub(mpdigit *b, int n, mpdigit m, mpdigit *p)

       void    mpvecmul(mpdigit *a, int alen, mpdigit *b, int blen,
               mpdigit *p)

       int     mpveccmp(mpdigit *a, int alen, mpdigit *b, int blen)

       CRTpre* crtpre(int nfactors, mpint **factors)

       CRTres* crtin(CRTpre *crt, mpint *x)

       void    crtout(CRTpre *crt, CRTres *r, mpint *x)

       void    crtprefree(CRTpre *cre)

       void    crtresfree(CRTres *res)

       mpint   *mpzero, *mpone, *mptwo

DESCRIPTION
       These routines perform  extended  precision  integer  arithmetic.   The
       basic  type  is  mpint, which points to an array of mpdigits, stored in
       little-endian order:

              typedef struct mpint mpint;
              struct mpint
              {
                   int  sign;   /* +1 or -1 */
                   int  size;   /* allocated digits */
                   int  top;    /* significant digits */
                   mpdigit   *p;
                   char flags;
              };

       The sign of 0 is +1.

       The  size  of  mpdigit  is  architecture-dependent   and   defined   in
       /$cputype/include/u.h.   Mpints  are  dynamically allocated and must be
       explicitly freed.  Operations grow the array of digits as needed.

       In general, the result parameters are last in the argument list.

       Routines that return an mpint will allocate the  mpint  if  the  result
       parameter  is  nil.   This  includes strtomp, itomp, uitomp, and btomp.
       These functions, in addition to mpnew and mpcopy, will  return  nil  if
       the allocation fails.

       Input  and result parameters may point to the same mpint.  The routines
       check and copy where necessary.

       Mpnew creates an mpint with an initial allocation of n bits.  If  n  is
       zero, the allocation will be whatever was specified in the last call to
       mpsetminbits or to the initial value, 1056.   Mpfree  frees  an  mpint.
       Mpbits  grows  the  allocation  of b to fit at least n bits.  If b->top
       doesn't cover n bits, mpbits increases it to do  so.   Unless  you  are
       writing new basic operations, you can restrict yourself to mpnew(0) and
       mpfree(b).

       Mpnorm normalizes the representation by trimming any  high  order  zero
       digits.  All routines except mpbits return normalized results.

       Mpcopy creates a new mpint with the same value as b while mpassign sets
       the value of new to be that of old.

       Mprand creates an n bit random number using  the  generator  gen.   Gen
       takes a pointer to a string of uchar's and the number to fill in.

       Strtomp and mptoa convert between ASCII and mpint representations using
       the base indicated.  Only the bases 10, 16, 32, and 64  are  supported.
       Anything  else  defaults  to  16.   Strtomp skips any leading spaces or
       tabs.  Strtomp's scan stops when encountering a digit not valid in  the
       base.   If  rptr  is  not  zero, *rptr is set to point to the character
       immediately after the  string  converted.   If  the  parse  pterminates
       before  any  digits  are  found,  strtomp  return nil.  Mptoa returns a
       pointer to the filled buffer.  If the parameter buf is nil, the  buffer
       is  allocated.   Mpfmt  can  be used with fmtinstall(2) and print(2) to
       print hexadecimal representations of mpints.  The conventional verb  is
       for which mp.h provides a

       Mptobe and mptole convert an mpint to a byte array.  The former creates
       a big endian representation, the latter a little endian  one.   If  the
       destination  buf is not nil, it specifies the buffer of length blen for
       the result.  If the representation is less than blen bytes, the rest of
       the  buffer  is zero filled.  If buf is nil, then a buffer is allocated
       and a pointer to it is deposited in the location pointed  to  by  bufp.
       Sign  is  ignored in these conversions, i.e., the byte array version is
       always positive.

       Betomp, and letomp convert from a big or little endian  byte  array  at
       buf of length blen to an mpint.  If b is not nil, it refers to a preal‐
       located mpint for the result.  If b is nil, a new integer is  allocated
       and returned as the result.

       The integer conversions are:

       mptoui mpint->unsigned int

       uitomp unsigned int->mpint

       mptoi  mpint->int

       itomp  int->mpint

       mptouv mpint->unsigned vlong

       uvtomp unsigned vlong->mpint

       mptov  mpint->vlong

       vtomp  vlong->mpint

       When converting to the base integer types, if the integer is too large,
       the largest integer of the appropriate sign and size is returned.

       The mathematical functions are:

       mpadd  sum = b1 + b2.

       mpmagadd
              sum = abs(b1) + abs(b2).

       mpsub  diff = b1 - b2.

       mpmagsub
              diff = abs(b1) - abs(b2).

       mpleft res = b<<shift.

       mpright
              res = b>>shift.

       mpmul  prod = b1*b2.

       mpexp  if m is nil, res = b**e.  Otherwise, res = b**e mod m.

       mpmod  remainder = b % m.

       mpdiv  quotient = dividend/divisor.  remainder = dividend % divisor.

       mpcmp  returns -1, 0, or +1 as b1 is less than, equal  to,  or  greater
              than b2.

       mpmagcmp
              the  same as mpcmp but ignores the sign and just compares magni‐
              tudes.

       Mpextendedgcd computes the greatest common denominator, d, of a and  b.
       It  also  computes  x  and y such that a*x + b*y = d.  Both a and b are
       required to be positive.  If called with negative  arguments,  it  will
       return a gcd of 0.

       Mpinverse computes the multiplicative inverse of b mod m.

       Mpsignif  returns  the  number  of  significant  bits in b.  Mplowbits0
       returns the number of consecutive zero bits at the low end of the  sig‐
       nificant  bits.   For  example, for 0x14, mpsignif returns 5 and mplow‐
       bits0 returns 2.  For 0, mpsignif and mplowbits0 both return 0.

       The remaining routines all  work  on  arrays  of  mpdigit  rather  than
       mpint's.  They are the basis of all the other routines.  They are sepa‐
       rated out to allow them to be rewritten in assembler for each architec‐
       ture.  There is also a portable C version for each one.

       mpdigdiv
              quotient = dividend[0:1] / divisor.

       mpvecadd
              sum[0:alen] = a[0:alen-1] + b[0:blen-1].  We assume alen >= blen
              and that sum has room for alen+1 digits.

       mpvecsub
              diff[0:alen-1] = a[0:alen-1] - b[0:blen-1].  We assume that alen
              >= blen and that diff has room for alen digits.

       mpvecdigmuladd
              p[0:n]  +=  m  * b[0:n-1].  This multiplies a an array of digits
              times a scalar and adds it to another array.  We  assume  p  has
              room for n+1 digits.

       mpvecdigmulsub
              p[0:n]  -=  m  * b[0:n-1].  This multiplies a an array of digits
              times a scalar and subtracts it fromo another array.  We  assume
              p has room for n+1 digits.  It returns +1 is the result is posi‐
              tive and -1 if negative.

       mpvecmul
              p[0:alen*blen] = a[0:alen-1] * b[0:blen-1].  We  assume  that  p
              has room for alen*blen+1 digits.

       mpveccmp
              This returns -1, 0, or +1 as a - b is negative, 0, or positive.

       mptwo,  mpone and mpzero are the constants 2, 1 and 0.  These cannot be
       freed.

   Chinese remainder theorem
       When computing in a non-prime modulus, n, it is possible to perform the
       computations  on  the  residues  modulo the prime factors of n instead.
       Since these numbers are smaller, multiplication and exponentiation  can
       be much faster.

       Crtin  computes the residues of x and returns them in a newly allocated
       structure:

              typedef struct CRTres    CRTres;
              {
                   int  n;   /* number of residues */
                   mpint     *r[n];    /* residues */
              };

       Crtout takes a residue representation of a number and converts it  back
       into the number.  It also frees the residue structure.

       Crepre saves a copy of the factors and precomputes the constants neces‐
       sary for converting the residue form back  into  a  number  modulo  the
       product  of  the  factors.  It returns a newly allocated structure con‐
       taining values.

       Crtprefree and crtresfree free CRTpre  and  CRTres  structures  respec‐
       tively.

SOURCE
       /sys/src/libmp



                                                                         MP(2)