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127 lines
2.4 KiB
C
127 lines
2.4 KiB
C
/*
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Copyright 1982
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Alcyon Corporation
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8716 Production Ave.
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San Diego, Ca. 92121
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*/
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/*char *version "@(#) atof - dec 29, 1982"; */
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/*
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* Ascii String to IEEE Floating Point Routine :
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* IEEE Standard Single Precision Representation Floating Point
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*
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* float
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* atof(buf)
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* char *buf;
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*
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* No more than 9 significant digits are allowed in single precision.
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* Largest positive number is 3.4 * 10^33 and the smallest positive
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* number is 1.2 * 10^-38.
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* Rely's on the fact that a long and a float are both 32 bits.
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*/
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#define BIAS 127L
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#define EXPSIZ 4
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#define FRACSIZ 20
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long fptoieee();
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float strbin();
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float power10();
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long
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atof(buf)
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char *buf;
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{
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char ibuf[FRACSIZ], ebuf[EXPSIZ];
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register char *ip, *ep;
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long ieee; /* return value */
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int dp, esign, isign, ebin, places;
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float ibin, fp;
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ip = &ibuf; ep = &ebuf; dp = 0; places = 0L;
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while (*buf == ' ' || *buf == '\t') /* ignore white spaces */
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buf++;
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isign = (*buf == '-');
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if (*buf == '-' || *buf == '+')
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buf++;
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while (*buf && *buf != 'e' && *buf != 'E') {
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if (*buf == '.')
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dp++;
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else { /* digit seen */
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*ip++ = *buf;
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if (dp)
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places++;
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}
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buf++;
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}
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*ip = 0;
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if (*buf == 'e' || *buf == 'E') { /* exponent string */
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buf++;
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esign = (*buf == '-');
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if (*buf == '-' || *buf == '+')
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buf++;
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while (*buf) /* get exponent string */
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*ep++ = *buf++;
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}
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*ep = 0;
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ibin = strbin(ibuf);
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ebin = atoi(ebuf);
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places = (esign) ? -ebin - places : ebin - places;
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fp = ibin * power10(places);
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ieee = fptoieee(fp);
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if (isign) /* negative float */
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ieee =| 0x80000000;
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return( ieee );
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}
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float
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power10(pwr) /* 10^pwr */
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int pwr;
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{
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float f;
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if (pwr < 0L) /* negative power */
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for (f = 1.0; pwr < 0; pwr++)
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f = f / 10.0;
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else /* positive power */
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for (f = 1.0; pwr > 0; pwr--)
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f = f * 10.0;
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return(f);
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}
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long
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fptoieee(f) /* convert current machine float to ieee rep */
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float f; /* unsigned float... */
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{
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register long exp, l;
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if (f == 0.0)
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return(0L);
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exp = 0L;
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for( ; f >= 2.0; f = f / 2.0)
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exp++;
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for( ; f < 1.0; f = f * 2.0)
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exp--;
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f = f - 1.0; /* implicit 1, eg. 1.F */
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if (f != 0.0)
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f = f * 8388608.0; /* 2 ^ 23 */
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l = f;
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exp =+ BIAS;
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l =| ((exp<<23) & 0x7f800000);
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return(l);
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}
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float
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strbin(p) /* decimal string => binary long */
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char *p;
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{
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float f;
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for (f = 0.0; *p >= '0' && *p <= '9'; p++) {
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f = f * 10.0;
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f = f + (*p - '0');
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}
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return(f);
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}
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