Make improvements

third_party/gdtoa/strtodnrp.c

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+#include "third_party/gdtoa/gdtoaimp.h"
+
+/* clang-format off */
+/****************************************************************
+
+The author of this software is David M. Gay.
+
+Copyright (C) 2004 by David M. Gay.
+All Rights Reserved
+Based on material in the rest of /netlib/fp/gdota.tar.gz,
+which is copyright (C) 1998, 2000 by Lucent Technologies.
+
+Permission to use, copy, modify, and distribute this software and
+its documentation for any purpose and without fee is hereby
+granted, provided that the above copyright notice appear in all
+copies and that both that the copyright notice and this
+permission notice and warranty disclaimer appear in supporting
+documentation, and that the name of Lucent or any of its entities
+not be used in advertising or publicity pertaining to
+distribution of the software without specific, written prior
+permission.
+
+LUCENT DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS.
+IN NO EVENT SHALL LUCENT OR ANY OF ITS ENTITIES BE LIABLE FOR ANY
+SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER
+IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
+ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.
+
+****************************************************************/
+
+/* This is a variant of strtod that works on Intel ia32 systems */
+/* with the default extended-precision arithmetic -- it does not */
+/* require setting the precision control to 53 bits.  */
+
+/* Please send bug reports to David M. Gay (dmg at acm dot org,
+ * with " at " changed at "@" and " dot " changed to ".").	*/
+
+ double
+#ifdef KR_headers
+strtod(s, sp) CONST char *s; char **sp;
+#else
+strtod(CONST char *s, char **sp)
+#endif
+{
+	static const FPI fpi = { 53, 1-1023-53+1, 2046-1023-53+1, 1, SI, 0 /*unused*/ };
+	ULong bits[2];
+	Long exp;
+	int k;
+	union { ULong L[2]; double d; } u;
+
+	k = strtodg(s, sp, &fpi, &exp, bits);
+	switch(k & STRTOG_Retmask) {
+	  case STRTOG_NoNumber:
+	  case STRTOG_Zero:
+		u.L[0] = u.L[1] = 0;
+		break;
+
+	  case STRTOG_Normal:
+		u.L[_1] = bits[0];
+		u.L[_0] = (bits[1] & ~0x100000) | ((exp + 0x3ff + 52) << 20);
+		break;
+
+	  case STRTOG_Denormal:
+		u.L[_1] = bits[0];
+		u.L[_0] = bits[1];
+		break;
+
+	  case STRTOG_Infinite:
+		u.L[_0] = 0x7ff00000;
+		u.L[_1] = 0;
+		break;
+
+	  case STRTOG_NaN:
+		u.L[0] = d_QNAN0;
+		u.L[1] = d_QNAN1;
+		break;
+
+	  case STRTOG_NaNbits:
+		u.L[_0] = 0x7ff00000 | bits[1];
+		u.L[_1] = bits[0];
+	  }
+	if (k & STRTOG_Neg)
+		u.L[_0] |= 0x80000000L;
+	return u.d;
+	}