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416 lines
11 KiB
C
416 lines
11 KiB
C
/* atof_tahoe.c - turn a string into a Tahoe floating point number
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Copyright (C) 1987, 1998 Free Software Foundation, Inc. */
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/* This is really a simplified version of atof_vax.c. I glommed it wholesale
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and then shaved it down. I don't even know how it works. (Don't you find
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my honesty refreshing? Devon E Bowen <bowen@cs.buffalo.edu>
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I don't allow uppercase letters in the precision descrpitors.
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i.e. 'f' and 'd' are allowed but 'F' and 'D' aren't. */
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#include "as.h"
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/* Precision in LittleNums. */
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#define MAX_PRECISION (4)
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#define D_PRECISION (4)
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#define F_PRECISION (2)
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/* Precision in chars. */
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#define D_PRECISION_CHARS (8)
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#define F_PRECISION_CHARS (4)
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/* Length in LittleNums of guard bits. */
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#define GUARD (2)
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static const long int mask[] =
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{
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0x00000000,
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0x00000001,
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0x00000003,
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0x00000007,
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0x0000000f,
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0x0000001f,
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0x0000003f,
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0x0000007f,
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0x000000ff,
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0x000001ff,
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0x000003ff,
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0x000007ff,
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0x00000fff,
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0x00001fff,
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0x00003fff,
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0x00007fff,
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0x0000ffff,
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0x0001ffff,
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0x0003ffff,
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0x0007ffff,
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0x000fffff,
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0x001fffff,
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0x003fffff,
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0x007fffff,
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0x00ffffff,
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0x01ffffff,
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0x03ffffff,
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0x07ffffff,
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0x0fffffff,
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0x1fffffff,
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0x3fffffff,
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0x7fffffff,
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0xffffffff
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};
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/* Shared between flonum_gen2tahoe and next_bits. */
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static int bits_left_in_littlenum;
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static LITTLENUM_TYPE *littlenum_pointer;
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static LITTLENUM_TYPE *littlenum_end;
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#if __STDC__ == 1
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int flonum_gen2tahoe (int format_letter, FLONUM_TYPE * f,
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LITTLENUM_TYPE * words);
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#else /* not __STDC__ */
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int flonum_gen2tahoe ();
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#endif /* not __STDC__ */
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static int
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next_bits (number_of_bits)
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int number_of_bits;
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{
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int return_value;
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if (littlenum_pointer < littlenum_end)
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return 0;
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if (number_of_bits >= bits_left_in_littlenum)
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{
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return_value = mask[bits_left_in_littlenum] & *littlenum_pointer;
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number_of_bits -= bits_left_in_littlenum;
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return_value <<= number_of_bits;
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bits_left_in_littlenum = LITTLENUM_NUMBER_OF_BITS - number_of_bits;
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littlenum_pointer--;
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if (littlenum_pointer >= littlenum_end)
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return_value |= ((*littlenum_pointer) >> (bits_left_in_littlenum)) &
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mask[number_of_bits];
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}
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else
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{
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bits_left_in_littlenum -= number_of_bits;
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return_value = mask[number_of_bits] &
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((*littlenum_pointer) >> bits_left_in_littlenum);
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}
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return return_value;
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}
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static void
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make_invalid_floating_point_number (words)
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LITTLENUM_TYPE *words;
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{
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/* Floating Reserved Operand Code. */
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*words = 0x8000;
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}
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static int /* 0 means letter is OK. */
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what_kind_of_float (letter, precisionP, exponent_bitsP)
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/* In: lowercase please. What kind of float? */
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char letter;
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/* Number of 16-bit words in the float. */
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int *precisionP;
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/* Number of exponent bits. */
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long int *exponent_bitsP;
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{
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int retval; /* 0: OK. */
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retval = 0;
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switch (letter)
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{
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case 'f':
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*precisionP = F_PRECISION;
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*exponent_bitsP = 8;
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break;
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case 'd':
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*precisionP = D_PRECISION;
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*exponent_bitsP = 8;
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break;
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default:
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retval = 69;
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break;
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}
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return (retval);
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}
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/* Warning: This returns 16-bit LITTLENUMs, because that is what the
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VAX thinks in. It is up to the caller to figure out any alignment
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problems and to conspire for the bytes/word to be emitted in the
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right order. Bigendians beware! */
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char * /* Return pointer past text consumed. */
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atof_tahoe (str, what_kind, words)
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char *str; /* Text to convert to binary. */
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char what_kind; /* 'd', 'f', 'g', 'h' */
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LITTLENUM_TYPE *words; /* Build the binary here. */
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{
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FLONUM_TYPE f;
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LITTLENUM_TYPE bits[MAX_PRECISION + MAX_PRECISION + GUARD];
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/* Extra bits for zeroed low-order bits. */
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/* The 1st MAX_PRECISION are zeroed, the last contain flonum bits. */
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char *return_value;
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int precision; /* Number of 16-bit words in the format. */
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long int exponent_bits;
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return_value = str;
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f.low = bits + MAX_PRECISION;
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f.high = NULL;
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f.leader = NULL;
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f.exponent = NULL;
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f.sign = '\0';
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if (what_kind_of_float (what_kind, &precision, &exponent_bits))
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{
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/* We lost. */
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return_value = NULL;
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make_invalid_floating_point_number (words);
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}
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if (return_value)
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{
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memset (bits, '\0', sizeof (LITTLENUM_TYPE) * MAX_PRECISION);
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/* Use more LittleNums than seems necessary:
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the highest flonum may have 15 leading 0 bits, so could be
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useless. */
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f.high = f.low + precision - 1 + GUARD;
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if (atof_generic (&return_value, ".", "eE", &f))
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{
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make_invalid_floating_point_number (words);
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/* We lost. */
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return_value = NULL;
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}
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else
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{
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if (flonum_gen2tahoe (what_kind, &f, words))
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return_value = NULL;
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}
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}
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return return_value;
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}
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/* In: a flonum, a Tahoe floating point format.
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Out: a Tahoe floating-point bit pattern. */
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int /* 0: OK. */
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flonum_gen2tahoe (format_letter, f, words)
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char format_letter; /* One of 'd' 'f'. */
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FLONUM_TYPE *f;
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LITTLENUM_TYPE *words; /* Deliver answer here. */
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{
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LITTLENUM_TYPE *lp;
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int precision;
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long int exponent_bits;
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int return_value; /* 0 == OK. */
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return_value =
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what_kind_of_float (format_letter, &precision, &exponent_bits);
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if (return_value != 0)
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{
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make_invalid_floating_point_number (words);
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}
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else
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{
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if (f->low > f->leader)
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{
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/* 0.0e0 seen. */
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memset (words, '\0', sizeof (LITTLENUM_TYPE) * precision);
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}
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else
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{
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long int exponent_1;
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long int exponent_2;
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long int exponent_3;
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long int exponent_4;
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int exponent_skippage;
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LITTLENUM_TYPE word1;
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/* JF: Deal with new Nan, +Inf and -Inf codes. */
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if (f->sign != '-' && f->sign != '+')
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{
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make_invalid_floating_point_number (words);
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return return_value;
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}
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/* All tahoe floating_point formats have:
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Bit 15 is sign bit.
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Bits 14:n are excess-whatever exponent.
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Bits n-1:0 (if any) are most significant bits of fraction.
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Bits 15:0 of the next word are the next most significant bits.
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And so on for each other word.
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So we need: number of bits of exponent, number of bits of
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mantissa. */
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bits_left_in_littlenum = LITTLENUM_NUMBER_OF_BITS;
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littlenum_pointer = f->leader;
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littlenum_end = f->low;
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/* Seek (and forget) 1st significant bit. */
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for (exponent_skippage = 0;
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!next_bits (1);
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exponent_skippage++)
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;
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exponent_1 = f->exponent + f->leader + 1 - f->low;
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/* Radix LITTLENUM_RADIX, point just higher than f -> leader. */
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exponent_2 = exponent_1 * LITTLENUM_NUMBER_OF_BITS;
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/* Radix 2. */
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exponent_3 = exponent_2 - exponent_skippage;
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/* Forget leading zeros, forget 1st bit. */
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exponent_4 = exponent_3 + (1 << (exponent_bits - 1));
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/* Offset exponent. */
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if (exponent_4 & ~mask[exponent_bits])
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{
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/* Exponent overflow. Lose immediately. */
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make_invalid_floating_point_number (words);
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/* We leave return_value alone: admit we read the
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number, but return a floating exception because we
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can't encode the number. */
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}
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else
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{
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lp = words;
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/* Word 1. Sign, exponent and perhaps high bits. */
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/* Assume 2's complement integers. */
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word1 = ((exponent_4 & mask[exponent_bits])
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<< (15 - exponent_bits))
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| ((f->sign == '+') ? 0 : 0x8000)
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| next_bits (15 - exponent_bits);
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*lp++ = word1;
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/* The rest of the words are just mantissa bits. */
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for (; lp < words + precision; lp++)
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*lp = next_bits (LITTLENUM_NUMBER_OF_BITS);
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if (next_bits (1))
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{
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/* Since the NEXT bit is a 1, round UP the mantissa.
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The cunning design of these hidden-1 floats permits
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us to let the mantissa overflow into the exponent, and
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it 'does the right thing'. However, we lose if the
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highest-order bit of the lowest-order word flips.
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Is that clear? */
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unsigned long int carry;
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/* #if (sizeof(carry)) < ((sizeof(bits[0]) *
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BITS_PER_CHAR) + 2) Please allow at least 1 more
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bit in carry than is in a LITTLENUM. We need
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that extra bit to hold a carry during a LITTLENUM
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carry propagation. Another extra bit (kept 0)
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will assure us that we don't get a sticky sign
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bit after shifting right, and that permits us to
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propagate the carry without any masking of bits.
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#endif */
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for (carry = 1, lp--;
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carry && (lp >= words);
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lp--)
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{
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carry = *lp + carry;
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*lp = carry;
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carry >>= LITTLENUM_NUMBER_OF_BITS;
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}
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if ((word1 ^ *words)
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& (1 << (LITTLENUM_NUMBER_OF_BITS - 1)))
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{
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make_invalid_floating_point_number (words);
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/* We leave return_value alone: admit we read
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the number, but return a floating exception
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because we can't encode the number. */
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}
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} /* if (we needed to round up) */
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} /* if (exponent overflow) */
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} /* if (0.0e0) */
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} /* if (float_type was OK) */
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return return_value;
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}
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/* In: input_line_pointer -> the 1st character of a floating-point
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* number.
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* 1 letter denoting the type of statement that wants a
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* binary floating point number returned.
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* Address of where to build floating point literal.
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* Assumed to be 'big enough'.
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* Address of where to return size of literal (in chars).
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*
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* Out: Input_line_pointer -> of next char after floating number.
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* Error message, or 0.
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* Floating point literal.
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* Number of chars we used for the literal. */
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char *
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md_atof (what_statement_type, literalP, sizeP)
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char what_statement_type;
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char *literalP;
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int *sizeP;
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{
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LITTLENUM_TYPE words[MAX_PRECISION];
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register char kind_of_float;
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register int number_of_chars;
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register LITTLENUM_TYPE *littlenum_pointer;
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switch (what_statement_type)
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{
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case 'f': /* .ffloat */
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case 'd': /* .dfloat */
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kind_of_float = what_statement_type;
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break;
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default:
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kind_of_float = 0;
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break;
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}
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if (kind_of_float)
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{
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register LITTLENUM_TYPE *limit;
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input_line_pointer = atof_tahoe (input_line_pointer,
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kind_of_float,
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words);
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/* The atof_tahoe() builds up 16-bit numbers.
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Since the assembler may not be running on
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a different-endian machine, be very careful about
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converting words to chars. */
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number_of_chars = (kind_of_float == 'f' ? F_PRECISION_CHARS :
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(kind_of_float == 'd' ? D_PRECISION_CHARS : 0));
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know (number_of_chars <= MAX_PRECISION * sizeof (LITTLENUM_TYPE));
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limit = words + (number_of_chars / sizeof (LITTLENUM_TYPE));
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for (littlenum_pointer = words;
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littlenum_pointer < limit;
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littlenum_pointer++)
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{
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md_number_to_chars (literalP, *littlenum_pointer,
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sizeof (LITTLENUM_TYPE));
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literalP += sizeof (LITTLENUM_TYPE);
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}
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}
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else
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{
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number_of_chars = 0;
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}
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*sizeP = number_of_chars;
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return kind_of_float ? 0 : _("Bad call to md_atof()");
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}
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