From a77bbddc836a30e81c3fa8549efa8e52769c8725 Mon Sep 17 00:00:00 2001 From: Mark Dickinson Date: Wed, 18 Mar 2009 20:06:12 +0000 Subject: Issue #4258: Make it possible to use 30-bit digits for PyLongs: - new configure option --enable-big-digits - new structseq sys.int_info giving information about the internal format By default, 30-bit digits are enabled on 64-bit machines but disabled on 32-bit machines. --- Include/longintrepr.h | 68 +++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 53 insertions(+), 15 deletions(-) (limited to 'Include/longintrepr.h') diff --git a/Include/longintrepr.h b/Include/longintrepr.h index 2dbb3f5296..144d04b8dd 100644 --- a/Include/longintrepr.h +++ b/Include/longintrepr.h @@ -7,24 +7,62 @@ extern "C" { /* This is published for the benefit of "friend" marshal.c only. */ -/* Parameters of the long integer representation. - These shouldn't have to be changed as C should guarantee that a short - contains at least 16 bits, but it's made changeable anyway. - Note: 'digit' should be able to hold 2*MASK+1, and 'twodigits' - should be able to hold the intermediate results in 'mul' - (at most (BASE-1)*(2*BASE+1) == MASK*(2*MASK+3)). - Also, x_sub assumes that 'digit' is an unsigned type, and overflow - is handled by taking the result mod 2**N for some N > SHIFT. - And, at some places it is assumed that MASK fits in an int, as well. - long_pow() requires that SHIFT be divisible by 5. */ +/* Parameters of the long integer representation. There are two different + sets of parameters: one set for 30-bit digits, stored in an unsigned 32-bit + integer type, and one set for 15-bit digits with each digit stored in an + unsigned short. The value of PYLONG_BITS_IN_DIGIT, defined either at + configure time or in pyport.h, is used to decide which digit size to use. -typedef unsigned short digit; -typedef short sdigit; /* signed variant of digit */ -#define BASE_TWODIGITS_TYPE long -typedef unsigned BASE_TWODIGITS_TYPE twodigits; -typedef BASE_TWODIGITS_TYPE stwodigits; /* signed variant of twodigits */ + Type 'digit' should be able to hold 2*PyLong_BASE-1, and type 'twodigits' + should be an unsigned integer type able to hold all integers up to + PyLong_BASE*PyLong_BASE-1. x_sub assumes that 'digit' is an unsigned type, + and that overflow is handled by taking the result modulo 2**N for some N > + PyLong_SHIFT. The majority of the code doesn't care about the precise + value of PyLong_SHIFT, but there are some notable exceptions: + + - long_pow() requires that PyLong_SHIFT be divisible by 5 + + - PyLong_{As,From}ByteArray require that PyLong_SHIFT be at least 8 + + - long_hash() requires that PyLong_SHIFT is *strictly* less than the number + of bits in an unsigned long, as do the PyLong <-> long (or unsigned long) + conversion functions + + - the long <-> size_t/Py_ssize_t conversion functions expect that + PyLong_SHIFT is strictly less than the number of bits in a size_t + + - the marshal code currently expects that PyLong_SHIFT is a multiple of 15 + + - NSMALLNEGINTS and NSMALLPOSINTS should be small enough to fit in a single + digit; with the current values this forces PyLong_SHIFT >= 9 + The values 15 and 30 should fit all of the above requirements, on any + platform. +*/ + +#if HAVE_STDINT_H +#include +#endif + +#if PYLONG_BITS_IN_DIGIT == 30 +#if !(defined HAVE_UINT64_T && defined HAVE_UINT32_T && \ + defined HAVE_INT64_T && defined HAVE_INT32_T) +#error "30-bit long digits requested, but the necessary types are not available on this platform" +#endif +typedef PY_UINT32_T digit; +typedef PY_INT32_T sdigit; /* signed variant of digit */ +typedef PY_UINT64_T twodigits; +typedef PY_INT64_T stwodigits; /* signed variant of twodigits */ +#define PyLong_SHIFT 30 +#elif PYLONG_BITS_IN_DIGIT == 15 +typedef unsigned short digit; +typedef short sdigit; /* signed variant of digit */ +typedef unsigned long twodigits; +typedef long stwodigits; /* signed variant of twodigits */ #define PyLong_SHIFT 15 +#else +#error "PYLONG_BITS_IN_DIGIT should be 15 or 30" +#endif #define PyLong_BASE ((digit)1 << PyLong_SHIFT) #define PyLong_MASK ((digit)(PyLong_BASE - 1)) -- cgit v1.2.1