ext/misc/ieee754.c

   1 /*
   2 ** 2013-04-17
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 ******************************************************************************
  12 **
  13 ** This SQLite extension implements functions for the exact display
  14 ** and input of IEEE754 Binary64 floating-point numbers.
  15 **
  16 **   ieee754(X)
  17 **   ieee754(Y,Z)
  18 **
  19 ** In the first form, the value X should be a floating-point number.
  20 ** The function will return a string of the form 'ieee754(Y,Z)' where
  21 ** Y and Z are integers such that X==Y*pow(2,Z).
  22 **
  23 ** In the second form, Y and Z are integers which are the mantissa and
  24 ** base-2 exponent of a new floating point number.  The function returns
  25 ** a floating-point value equal to Y*pow(2,Z).
  26 **
  27 ** Examples:
  28 **
  29 **     ieee754(2.0)             ->     'ieee754(2,0)'
  30 **     ieee754(45.25)           ->     'ieee754(181,-2)'
  31 **     ieee754(2, 0)            ->     2.0
  32 **     ieee754(181, -2)         ->     45.25
  33 **
  34 ** Two additional functions break apart the one-argument ieee754()
  35 ** result into separate integer values:
  36 **
  37 **     ieee754_mantissa(45.25)  ->     181
  38 **     ieee754_exponent(45.25)  ->     -2
  39 **
  40 ** These functions convert binary64 numbers into blobs and back again.
  41 **
  42 **     ieee754_from_blob(x'3ff0000000000000')  ->  1.0
  43 **     ieee754_to_blob(1.0)                    ->  x'3ff0000000000000'
  44 **
  45 ** In all single-argument functions, if the argument is an 8-byte blob
  46 ** then that blob is interpreted as a big-endian binary64 value.
  47 **
  48 **
  49 ** EXACT DECIMAL REPRESENTATION OF BINARY64 VALUES
  50 ** -----------------------------------------------
  51 **
  52 ** This extension in combination with the separate 'decimal' extension
  53 ** can be used to compute the exact decimal representation of binary64
  54 ** values.  To begin, first compute a table of exponent values:
  55 **
  56 **    CREATE TABLE pow2(x INTEGER PRIMARY KEY, v TEXT);
  57 **    WITH RECURSIVE c(x,v) AS (
  58 **      VALUES(0,'1')
  59 **      UNION ALL
  60 **      SELECT x+1, decimal_mul(v,'2') FROM c WHERE x+1<=971
  61 **    ) INSERT INTO pow2(x,v) SELECT x, v FROM c;
  62 **    WITH RECURSIVE c(x,v) AS (
  63 **      VALUES(-1,'0.5')
  64 **      UNION ALL
  65 **      SELECT x-1, decimal_mul(v,'0.5') FROM c WHERE x-1>=-1075
  66 **    ) INSERT INTO pow2(x,v) SELECT x, v FROM c;
  67 **
  68 ** Then, to compute the exact decimal representation of a floating
  69 ** point value (the value 47.49 is used in the example) do:
  70 **
  71 **    WITH c(n) AS (VALUES(47.49))
  72 **          ---------------^^^^^---- Replace with whatever you want
  73 **    SELECT decimal_mul(ieee754_mantissa(c.n),pow2.v)
  74 **      FROM pow2, c WHERE pow2.x=ieee754_exponent(c.n);
  75 **
  76 ** Here is a query to show various boundry values for the binary64
  77 ** number format:
  78 **
  79 **    WITH c(name,bin) AS (VALUES
  80 **       ('minimum positive value',        x'0000000000000001'),
  81 **       ('maximum subnormal value',       x'000fffffffffffff'),
  82 **       ('mininum positive nornal value', x'0010000000000000'),
  83 **       ('maximum value',                 x'7fefffffffffffff'))
  84 **    SELECT c.name, decimal_mul(ieee754_mantissa(c.bin),pow2.v)
  85 **      FROM pow2, c WHERE pow2.x=ieee754_exponent(c.bin);
  86 **
  87 */
  88 #include "sqlite3ext.h"
  89 SQLITE_EXTENSION_INIT1
  90 #include <assert.h>
  91 #include <string.h>
  92
  93 /* Mark a function parameter as unused, to suppress nuisance compiler
  94 ** warnings. */
  95 #ifndef UNUSED_PARAMETER
  96 # define UNUSED_PARAMETER(X)  (void)(X)
  97 #endif
  98
  99 /*
 100 ** Implementation of the ieee754() function
 101 */
 102 static void ieee754func(
 103   sqlite3_context *context,
 104   int argc,
 105   sqlite3_value **argv
 106 ){
 107   if( argc==1 ){
 108     sqlite3_int64 m, a;
 109     double r;
 110     int e;
 111     int isNeg;
 112     char zResult[100];
 113     assert( sizeof(m)==sizeof(r) );
 114     if( sqlite3_value_type(argv[0])==SQLITE_BLOB
 115      && sqlite3_value_bytes(argv[0])==sizeof(r)
 116     ){
 117       const unsigned char *x = sqlite3_value_blob(argv[0]);
 118       unsigned int i;
 119       sqlite3_uint64 v = 0;
 120       for(i=0; i<sizeof(r); i++){
 121         v = (v<<8) | x[i];
 122       }
 123       memcpy(&r, &v, sizeof(r));
 124     }else{
 125       r = sqlite3_value_double(argv[0]);
 126     }
 127     if( r<0.0 ){
 128       isNeg = 1;
 129       r = -r;
 130     }else{
 131       isNeg = 0;
 132     }
 133     memcpy(&a,&r,sizeof(a));
 134     if( a==0 ){
 135       e = 0;
 136       m = 0;
 137     }else{
 138       e = a>>52;
 139       m = a & ((((sqlite3_int64)1)<<52)-1);
 140       if( e==0 ){
 141         m <<= 1;
 142       }else{
 143         m |= ((sqlite3_int64)1)<<52;
 144       }
 145       while( e<1075 && m>0 && (m&1)==0 ){
 146         m >>= 1;
 147         e++;
 148       }
 149       if( isNeg ) m = -m;
 150     }
 151     switch( *(int*)sqlite3_user_data(context) ){
 152       case 0:
 153         sqlite3_snprintf(sizeof(zResult), zResult, "ieee754(%lld,%d)",
 154                          m, e-1075);
 155         sqlite3_result_text(context, zResult, -1, SQLITE_TRANSIENT);
 156         break;
 157       case 1:
 158         sqlite3_result_int64(context, m);
 159         break;
 160       case 2:
 161         sqlite3_result_int(context, e-1075);
 162         break;
 163     }
 164   }else{
 165     sqlite3_int64 m, e, a;
 166     double r;
 167     int isNeg = 0;
 168     m = sqlite3_value_int64(argv[0]);
 169     e = sqlite3_value_int64(argv[1]);
 170
 171     /* Limit the range of e.  Ticket 22dea1cfdb9151e4 2021-03-02 */
 172     if( e>10000 ){
 173       e = 10000;
 174     }else if( e<-10000 ){
 175       e = -10000;
 176     }
 177
 178     if( m<0 ){
 179       isNeg = 1;
 180       m = -m;
 181       if( m<0 ) return;
 182     }else if( m==0 && e>-1000 && e<1000 ){
 183       sqlite3_result_double(context, 0.0);
 184       return;
 185     }
 186     while( (m>>32)&0xffe00000 ){
 187       m >>= 1;
 188       e++;
 189     }
 190     while( m!=0 && ((m>>32)&0xfff00000)==0 ){
 191       m <<= 1;
 192       e--;
 193     }
 194     e += 1075;
 195     if( e<=0 ){
 196       /* Subnormal */
 197       if( 1-e >= 64 ){
 198         m = 0;
 199       }else{
 200         m >>= 1-e;
 201       }
 202       e = 0;
 203     }else if( e>0x7ff ){
 204       e = 0x7ff;
 205     }
 206     a = m & ((((sqlite3_int64)1)<<52)-1);
 207     a |= e<<52;
 208     if( isNeg ) a |= ((sqlite3_uint64)1)<<63;
 209     memcpy(&r, &a, sizeof(r));
 210     sqlite3_result_double(context, r);
 211   }
 212 }
 213
 214 /*
 215 ** Functions to convert between blobs and floats.
 216 */
 217 static void ieee754func_from_blob(
 218   sqlite3_context *context,
 219   int argc,
 220   sqlite3_value **argv
 221 ){
 222   UNUSED_PARAMETER(argc);
 223   if( sqlite3_value_type(argv[0])==SQLITE_BLOB
 224    && sqlite3_value_bytes(argv[0])==sizeof(double)
 225   ){
 226     double r;
 227     const unsigned char *x = sqlite3_value_blob(argv[0]);
 228     unsigned int i;
 229     sqlite3_uint64 v = 0;
 230     for(i=0; i<sizeof(r); i++){
 231       v = (v<<8) | x[i];
 232     }
 233     memcpy(&r, &v, sizeof(r));
 234     sqlite3_result_double(context, r);
 235   }
 236 }
 237 static void ieee754func_to_blob(
 238   sqlite3_context *context,
 239   int argc,
 240   sqlite3_value **argv
 241 ){
 242   UNUSED_PARAMETER(argc);
 243   if( sqlite3_value_type(argv[0])==SQLITE_FLOAT
 244    || sqlite3_value_type(argv[0])==SQLITE_INTEGER
 245   ){
 246     double r = sqlite3_value_double(argv[0]);
 247     sqlite3_uint64 v;
 248     unsigned char a[sizeof(r)];
 249     unsigned int i;
 250     memcpy(&v, &r, sizeof(r));
 251     for(i=1; i<=sizeof(r); i++){
 252       a[sizeof(r)-i] = v&0xff;
 253       v >>= 8;
 254     }
 255     sqlite3_result_blob(context, a, sizeof(r), SQLITE_TRANSIENT);
 256   }
 257 }
 258
 259
 260 #ifdef _WIN32
 261 __declspec(dllexport)
 262 #endif
 263 int sqlite3_ieee_init(
 264   sqlite3 *db,
 265   char **pzErrMsg,
 266   const sqlite3_api_routines *pApi
 267 ){
 268   static const struct {
 269     char *zFName;
 270     int nArg;
 271     int iAux;
 272     void (*xFunc)(sqlite3_context*,int,sqlite3_value**);
 273   } aFunc[] = {
 274     { "ieee754",           1,   0, ieee754func },
 275     { "ieee754",           2,   0, ieee754func },
 276     { "ieee754_mantissa",  1,   1, ieee754func },
 277     { "ieee754_exponent",  1,   2, ieee754func },
 278     { "ieee754_to_blob",   1,   0, ieee754func_to_blob },
 279     { "ieee754_from_blob", 1,   0, ieee754func_from_blob },
 280
 281   };
 282   unsigned int i;
 283   int rc = SQLITE_OK;
 284   SQLITE_EXTENSION_INIT2(pApi);
 285   (void)pzErrMsg;  /* Unused parameter */
 286   for(i=0; i<sizeof(aFunc)/sizeof(aFunc[0]) && rc==SQLITE_OK; i++){
 287     rc = sqlite3_create_function(db, aFunc[i].zFName, aFunc[i].nArg,
 288                                SQLITE_UTF8|SQLITE_INNOCUOUS,
 289                                (void*)&aFunc[i].iAux,
 290                                aFunc[i].xFunc, 0, 0);
 291   }
 292   return rc;
 293 }