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1.1 root 1: #ifndef __COMMON__LIMITS_H__
2: #define __COMMON__LIMITS_H__
3:
4: /*
5: * This header file is the internal equivalent of the ISO C Standard header
6: * file <limits.h>. It defines many similar constants that are useful in
7: * system headers for parameterising definitions based on such things as
8: * the representation ranges of various types, but the names of the constants
9: * are prefixed with underscores to stay in the implementation namespace.
10: *
11: * Rather than just stating the constants, we calculate then from a small
12: * set of fundamental parameters. Doing it this way will give the right
13: * results as long as your preprocessor and compiler understand that ISO C
14: * type rules. If they don't, well, this will tell you that.
15: *
16: * Note that the "fundamental" constants can be determined at run-time in
17: * a portable fashion, but since we need them for the preprocessor we must
18: * depend on someone running such a program and supplying them.
19: *
20: * The fundamental parameters:
21: * __CHAR_BIT The number of bits in a character. While most systems
22: * built in the 1990s have 8, others are possible.
23: * __SHORT_DIV The factor by which to divide the number of bits in
24: * an integer by to give the number of bits in a short.
25: * __TWOSCOMP This contains 1 if the representation is twos-
26: * complement for negative integers, 0 if we have a
27: * sign-magnitude or ones-complement machine.
28: * __CHAR_SIGNED 1 if characters are signed, undefined if they are
29: * unsigned.
30: *
31: * Parameters that can be inferred from the type system:
32: * __INT_BIT The number of bits in an integer.
33: * __LONG_BIT The number of bits in a long.
34: */
35:
36: #include <common/feature.h>
37:
38: #if __COHERENT__ || __BORLANDC__ || defined (GNUDOS)
39:
40: # define __CHAR_BIT 8
41: # define __TWOSCOMP 1
42:
43: #if '\x80' < 0
44: # define __CHAR_SIGNED 1
45: #endif
46:
47: # if __BORLANDC__
48: # define __SHORT_DIV 1
49: # else
50: # define __SHORT_DIV 2
51: # endif
52:
53: #else
54:
55: # error The fundamental parameters of this system are not known.
56:
57: #endif
58:
59: #define __TOP_BIT_INT(bytes) (1U << (__CHAR_BIT * (bytes) - 1))
60: #define __TOP_BIT_LONG(bytes) (1UL << (__CHAR_BIT * (bytes) - 1))
61:
62: #if (~ 0U ^ (~ 0U / 2)) == __TOP_BIT_INT(1)
63: # define __INT_BIT (1 * __CHAR_BIT)
64: #elif (~ 0U ^ (~ 0U / 2)) == __TOP_BIT_INT(2)
65: # define __INT_BIT (2 * __CHAR_BIT)
66: #elif (~ 0U ^ (~ 0U / 2)) == __TOP_BIT_INT(4)
67: # define __INT_BIT (4 * __CHAR_BIT)
68: #elif (~ 0U ^ (~ 0U / 2)) == __TOP_BIT_INT(8)
69: # define __INT_BIT (8 * __CHAR_BIT)
70: #else
71: # error Cannot determine number of bits per int.
72: #endif
73:
74: #if (~ 0UL ^ (~ 0UL / 2)) == __TOP_BIT_LONG(1)
75: # define __LONG_BIT (1 * __CHAR_BIT)
76: #elif (~ 0UL ^ (~ 0UL / 2)) == __TOP_BIT_LONG(2)
77: # define __LONG_BIT (2 * __CHAR_BIT)
78: #elif (~ 0UL ^ (~ 0UL / 2)) == __TOP_BIT_LONG(4)
79: # define __LONG_BIT (4 * __CHAR_BIT)
80: #elif (~ 0UL ^ (~ 0UL / 2)) == __TOP_BIT_LONG(8)
81: # define __LONG_BIT (8 * __CHAR_BIT)
82: #else
83: # error Cannot determine number of bits per long.
84: #endif
85:
86: #define __SHRT_BIT (__INT_BIT / __SHORT_DIV)
87:
88: #define __UCHAR_MAX ((1U << (__CHAR_BIT - 1)) + \
89: ((1U << (__CHAR_BIT - 1)) - 1))
90: #define __SCHAR_MAX ((1 << (__CHAR_BIT - 2)) + \
91: ((1 << (__CHAR_BIT - 2)) - 1))
92: #define __SCHAR_MIN (- __SCHAR_MAX - __TWOSCOMP)
93:
94: #if __CHAR_SIGNED
95: # define __CHAR_MAX __SCHAR_MAX
96: # define __CHAR_MIN __SCHAR_MIN
97: #else
98: # define __CHAR_MAX __UCHAR_MAX
99: # define __CHAR_MIN 0
100: #endif
101:
102: #define __USHRT_MAX ((1U << (__SHRT_BIT - 1)) + \
103: ((1U << (__SHRT_BIT - 1)) - 1))
104: #define __SHRT_MAX ((1 << (__SHRT_BIT - 2)) + \
105: ((1 << (__SHRT_BIT - 2)) - 1))
106: #define __SHRT_MIN (- __SHRT_MAX - __TWOSCOMP)
107:
108: #define __UINT_MAX ((1U << (__INT_BIT - 1)) + \
109: ((1U << (__INT_BIT - 1)) - 1))
110: #define __INT_MAX ((1 << (__INT_BIT - 2)) + \
111: ((1 << (__INT_BIT - 2)) - 1))
112: #define __INT_MIN (- __INT_MAX - __TWOSCOMP)
113:
114: #define __ULONG_MAX ((1U << (__LONG_BIT - 1)) + \
115: ((1U << (__LONG_BIT - 1)) - 1))
116: #define __LONG_MAX ((1 << (__LONG_BIT - 2)) + \
117: ((1 << (__LONG_BIT - 2)) - 1))
118: #define __LONG_MIN (- __LONG_MAX - __TWOSCOMP)
119:
120:
121: /*
122: * A fequent use of all the above shenanigans is to figure out a mapping from
123: * the C data types to machine 8/16/32-bit specific idioms, where the actual
124: * assignment of data types to machine widths is highly variable (perhaps even
125: * controlled by a compiler switch).
126: *
127: * Here we create standard aliases for the 8-bit-multiple cases, which careful
128: * programs can use token-pasting with to further parameterize things. If
129: * other macros use the __CONCAT... () facility from <sys/ccompat.h> to create
130: * type-encoded macro names, the extra level of indirection in the
131: * preprocessor that comes from using a concatenation macro will cause the
132: * following substitutions to be made before the final token is created, thus
133: * automagically mapping from types into word sizes.
134: *
135: * Because the following information is mainly used in token-pasting, please
136: * leave the decimal constants alone!
137: */
138:
139: #if __CHAR_BIT == 8
140: # define __CHAR 8
141: #endif
142:
143: #if __SHRT_BIT == 16
144: # define __SHORT 16
145: #elif __SHRT_BIT == 32
146: # define __SHORT 32
147: #endif
148:
149: #if __INT_BIT == 16
150: # define __INT 16
151: #elif __INT_BIT == 32
152: # define __INT 32
153: #elif __INT_BIT == 64
154: # define __INT 64
155: #endif
156:
157: #if __LONG_BIT == 32
158: # define __LONG 32
159: #elif __LONG_BIT == 64
160: # define __LONG 64
161: #endif
162:
163: #endif /* ! defined (__COMMON__LIMITS_H__) */
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