+ * #define MALLOC your_malloc, where your_malloc(n) acts like malloc(n)
+ * if memory is available and otherwise does something you deem
+ * appropriate. If MALLOC is undefined, malloc will be invoked
+ * directly -- and assumed always to succeed.
+ * #define Omit_Private_Memory to omit logic (added Jan. 1998) for making
+ * memory allocations from a private pool of memory when possible.
+ * When used, the private pool is PRIVATE_MEM bytes long: 2304 bytes,
+ * unless #defined to be a different length. This default length
+ * suffices to get rid of MALLOC calls except for unusual cases,
+ * such as decimal-to-binary conversion of a very long string of
+ * digits. The longest string dtoa can return is about 751 bytes
+ * long. For conversions by strtod of strings of 800 digits and
+ * all dtoa conversions in single-threaded executions with 8-byte
+ * pointers, PRIVATE_MEM >= 7400 appears to suffice; with 4-byte
+ * pointers, PRIVATE_MEM >= 7112 appears adequate.
+ * #define INFNAN_CHECK on IEEE systems to cause strtod to check for
+ * Infinity and NaN (case insensitively). On some systems (e.g.,
+ * some HP systems), it may be necessary to #define NAN_WORD0
+ * appropriately -- to the most significant word of a quiet NaN.
+ * (On HP Series 700/800 machines, -DNAN_WORD0=0x7ff40000 works.)
+ * When INFNAN_CHECK is #defined and No_Hex_NaN is not #defined,
+ * strtod also accepts (case insensitively) strings of the form
+ * NaN(x), where x is a string of hexadecimal digits and spaces;
+ * if there is only one string of hexadecimal digits, it is taken
+ * for the 52 fraction bits of the resulting NaN; if there are two
+ * or more strings of hex digits, the first is for the high 20 bits,
+ * the second and subsequent for the low 32 bits, with intervening
+ * white space ignored; but if this results in none of the 52
+ * fraction bits being on (an IEEE Infinity symbol), then NAN_WORD0
+ * and NAN_WORD1 are used instead.
+ * #define MULTIPLE_THREADS if the system offers preemptively scheduled
+ * multiple threads. In this case, you must provide (or suitably
+ * #define) two locks, acquired by ACQUIRE_DTOA_LOCK(n) and freed
+ * by FREE_DTOA_LOCK(n) for n = 0 or 1. (The second lock, accessed
+ * in pow5mult, ensures lazy evaluation of only one copy of high
+ * powers of 5; omitting this lock would introduce a small
+ * probability of wasting memory, but would otherwise be harmless.)
+ * You must also invoke freedtoa(s) to free the value s returned by
+ * dtoa. You may do so whether or not MULTIPLE_THREADS is #defined.
+ * #define NO_IEEE_Scale to disable new (Feb. 1997) logic in strtod that
+ * avoids underflows on inputs whose result does not underflow.
+ * If you #define NO_IEEE_Scale on a machine that uses IEEE-format
+ * floating-point numbers and flushes underflows to zero rather
+ * than implementing gradual underflow, then you must also #define
+ * Sudden_Underflow.
+ * #define YES_ALIAS to permit aliasing certain double values with
+ * arrays of ULongs. This leads to slightly better code with
+ * some compilers and was always used prior to 19990916, but it
+ * is not strictly legal and can cause trouble with aggressively
+ * optimizing compilers (e.g., gcc 2.95.1 under -O2).
+ * #define USE_LOCALE to use the current locale's decimal_point value.
+ * #define SET_INEXACT if IEEE arithmetic is being used and extra
+ * computation should be done to set the inexact flag when the
+ * result is inexact and avoid setting inexact when the result
+ * is exact. In this case, dtoa.c must be compiled in
+ * an environment, perhaps provided by #include "dtoa.c" in a
+ * suitable wrapper, that defines two functions,
+ * int get_inexact(void);
+ * void clear_inexact(void);
+ * such that get_inexact() returns a nonzero value if the
+ * inexact bit is already set, and clear_inexact() sets the
+ * inexact bit to 0. When SET_INEXACT is #defined, strtod
+ * also does extra computations to set the underflow and overflow
+ * flags when appropriate (i.e., when the result is tiny and
+ * inexact or when it is a numeric value rounded to +-infinity).
+ * #define NO_ERRNO if strtod should not assign errno = ERANGE when
+ * the result overflows to +-Infinity or underflows to 0.