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 #include "sqlite3ext.h"
  35 SQLITE_EXTENSION_INIT1
  36 #include <assert.h>
  37 #include <string.h>
  38
  39 /*
  40 ** Implementation of the ieee754() function
  41 */
  42 static void ieee754func(
  43   sqlite3_context *context,
  44   int argc,
  45   sqlite3_value **argv
  46 ){
  47   if( argc==1 ){
  48     sqlite3_int64 m, a;
  49     double r;
  50     int e;
  51     int isNeg;
  52     char zResult[100];
  53     assert( sizeof(m)==sizeof(r) );
  54     if( sqlite3_value_type(argv[0])!=SQLITE_FLOAT ) return;
  55     r = sqlite3_value_double(argv[0]);
  56     if( r<0.0 ){
  57       isNeg = 1;
  58       r = -r;
  59     }else{
  60       isNeg = 0;
  61     }
  62     memcpy(&a,&r,sizeof(a));
  63     if( a==0 ){
  64       e = 0;
  65       m = 0;
  66     }else{
  67       e = a>>52;
  68       m = a & ((((sqlite3_int64)1)<<52)-1);
  69       m |= ((sqlite3_int64)1)<<52;
  70       while( e<1075 && m>0 && (m&1)==0 ){
  71         m >>= 1;
  72         e++;
  73       }
  74       if( isNeg ) m = -m;
  75     }
  76     sqlite3_snprintf(sizeof(zResult), zResult, "ieee754(%lld,%d)",
  77                      m, e-1075);
  78     sqlite3_result_text(context, zResult, -1, SQLITE_TRANSIENT);
  79   }else if( argc==2 ){
  80     sqlite3_int64 m, e, a;
  81     double r;
  82     int isNeg = 0;
  83     m = sqlite3_value_int64(argv[0]);
  84     e = sqlite3_value_int64(argv[1]);
  85     if( m<0 ){
  86       isNeg = 1;
  87       m = -m;
  88       if( m<0 ) return;
  89     }else if( m==0 && e>1000 && e<1000 ){
  90       sqlite3_result_double(context, 0.0);
  91       return;
  92     }
  93     while( (m>>32)&0xffe00000 ){
  94       m >>= 1;
  95       e++;
  96     }
  97     while( m!=0 && ((m>>32)&0xfff00000)==0 ){
  98       m <<= 1;
  99       e--;
 100     }
 101     e += 1075;
 102     if( e<0 ) e = m = 0;
 103     if( e>0x7ff ) e = 0x7ff;
 104     a = m & ((((sqlite3_int64)1)<<52)-1);
 105     a |= e<<52;
 106     if( isNeg ) a |= ((sqlite3_uint64)1)<<63;
 107     memcpy(&r, &a, sizeof(r));
 108     sqlite3_result_double(context, r);
 109   }
 110 }
 111
 112
 113 #ifdef _WIN32
 114 __declspec(dllexport)
 115 #endif
 116 int sqlite3_ieee_init(
 117   sqlite3 *db,
 118   char **pzErrMsg,
 119   const sqlite3_api_routines *pApi
 120 ){
 121   int rc = SQLITE_OK;
 122   SQLITE_EXTENSION_INIT2(pApi);
 123   (void)pzErrMsg;  /* Unused parameter */
 124   rc = sqlite3_create_function(db, "ieee754", 1, SQLITE_UTF8, 0,
 125                                ieee754func, 0, 0);
 126   if( rc==SQLITE_OK ){
 127     rc = sqlite3_create_function(db, "ieee754", 2, SQLITE_UTF8, 0,
 128                                  ieee754func, 0, 0);
 129   }
 130   return rc;
 131 }