��11-4 linux/kernel/math/convert.c

1 /*

2 * linux/kernel/math/convert.c

3 *

5 */

7 #include <linux/math_emu.h> // Э��ͷ�ļ��ʱʵ��ṹ��387�Ĵ��ȡ�

9 /*

10 * NOTE!!! There is some "non-obvious" optimisations in the temp_to_long

11 * and temp_to_short conversion routines: don't touch them if you don't

12 * know what's going on. They are the adding of one in the rounding: the

13 * overflow bit is also used for adding one into the exponent. Thus it

14 * looks like the overflow would be incorrectly handled, but due to the

15 * way the IEEE numbers work, things are correct.

16 *

17 * There is no checking for total overflow in the conversions, though (ie

18 * if the temp-real number simply won't fit in a short- or long-real.)

19 */

* ע��!!! ��temp_to_long��temp_to_short��ת��ӳ��Щ��ԡ�

* ��Ż��Ͳ�Ҫ��޸ġ��еļ�1��λҲͬ

* ��ָ��м�1��˿��ȥ��û�б��ȷ�ش��IEEE

* ��׼��涨��ݸ�ʽ�Ĳ��ʽ��Щ��ȷ�ġ�

* ��û�ж�ת��⣨Ҳ��ʱʵ��Ƿ��ܹ��򵥵ط��

* ʵ��ʵ��ʽ�У��

// ��ʵ��ת��ʱʵ��ʽ��

// ��ʵ��32λ��Ч��β��23λ��ָ��8λ��1��λ��

21 void short_to_temp(const short_real * a, temp_real * b)

22 {

// ��ȴ��ת��Ķ�ʵ��0��Ϊ0��ö�Ӧ��ʱʵ��b��Ч��Ϊ0��Ȼ��

// �ݶ�ʵ��λ��ʱʵ��ķ��λ��exponent��Чλ��

23 if (!(*a & 0x7fffffff)) {

24 b->a = b->b = 0; // ��ʱʵ��Ч�� = 0��

25 if (*a)

26 b->exponent = 0x8000; // ��÷��λ��

27 else

28 b->exponent = 0;

29 return;

30 }

// ��һ��ʵ��ȷ��Ӧ��ʱʵ��ָ��ֵ��Ҫ�õ��ƫ�ñ�ʾ��ĸ��

// ��ʵ��ָ��ƫ��127��ʱʵ��ָ��ƫ��16383��ȡ��ʵ��ָ��ֵ

// ��Ҫ��е�ƫ��Ϊ 16383�� ʱ��γ��ʱʵ��ʽ��ָ��ֵ exponent��⣬

// ��ʵ��Ǹ��Ҫ��ʱʵ��ķ��λ��λ79��һ��β��ֵ��ǰ�

// ��ʵ��8λ��23λβ��Чλ��ʱʵ��λ62��ʱʵ��β��λ63

// ��Ҫ��һ��1��Ҫ��0x80000000��ʱʵ��32λ��Ч��

31 b->exponent = ((*a>>23) & 0xff)-127+16383; // ȡ��ʵ��ָ��λ��ƫ��

32 if (*a<0)

33 b->exponent |= 0x8000; // ��Ϊ��÷��λ��

34 b->b = (*a<<8) | 0x80000000; // ��β��ӹ̶�1ֵ��

35 b->a = 0;

36 }

// ��ʵ��ת��ʱʵ��ʽ��

// ��short_to_temp()��ȫһ��ʵ��ָ��ƫ��1023��

38 void long_to_temp(const long_real * a, temp_real * b)

39 {

40 if (!a->a && !(a->b & 0x7fffffff)) {

41 b->a = b->b = 0; // ��ʱʵ��Ч�� = 0��

42 if (a->b)

43 b->exponent = 0x8000; // ��÷��λ��

44 else

45 b->exponent = 0;

46 return;

47 }

48 b->exponent = ((a->b >> 20) & 0x7ff)-1023+16383; // ȡ��ʵ��ָ��ƫ��

49 if (a->b<0)

50 b->exponent |= 0x8000; // ��Ϊ��÷��λ��

51 b->b = 0x80000000 | (a->b<<11) | (((unsigned long)a->a)>>21); // ��β��1��

52 b->a = a->a<<11;

53 }

// ��ʱʵ��ת��ɶ�ʵ��ʽ��

// ��short_to_temp()�෴��Ҫ��Ⱥ��⡣

55 void temp_to_short(const temp_real * a, short_real * b)

56 {

// ��ָ��Ϊ0��޷��λ��ö�ʵ��Ϊ-0 ��0��

57 if (!(a->exponent & 0x7fff)) {

58 *b = (a->exponent)?0x80000000:0;

59 return;

60 }

// �ȴ��ָ��֡��ʱʵ��ָ��ƫ��16383��Ϊ��ʵ��ƫ��127��

61 *b = ((((long) a->exponent)-16383+127) << 23) & 0x7f800000;

62 if (a->exponent < 0) // ��Ǹ��÷��λ��

63 *b |= 0x80000000;

64 *b |= (a->b >> 8) & 0x007fffff; // ȡ��ʱʵ��Ч��23λ��

// ��ݿ��е��ִ��

65 switch (ROUNDING) {

66 case ROUND_NEAREST:

67 if ((a->b & 0xff) > 0x80)

68 ++*b;

69 break;

70 case ROUND_DOWN:

71 if ((a->exponent & 0x8000) && (a->b & 0xff))

72 ++*b;

73 break;

74 case ROUND_UP:

75 if (!(a->exponent & 0x8000) && (a->b & 0xff))

76 ++*b;

77 break;

78 }

79 }

// ��ʱʵ��ת��ɳ�ʵ��

81 void temp_to_long(const temp_real * a, long_real * b)

82 {

83 if (!(a->exponent & 0x7fff)) {

84 b->a = 0;

85 b->b = (a->exponent)?0x80000000:0;

86 return;

87 }

88 b->b = (((0x7fff & (long) a->exponent)-16383+1023) << 20) & 0x7ff00000;

89 if (a->exponent < 0)

90 b->b |= 0x80000000;

91 b->b |= (a->b >> 11) & 0x000fffff;

92 b->a = a->b << 21;

93 b->a |= (a->a >> 11) & 0x001fffff;

94 switch (ROUNDING) {

95 case ROUND_NEAREST:

96 if ((a->a & 0x7ff) > 0x400)

97 __asm__("addl $1,%0 ; adcl $0,%1"

98 :"=r" (b->a),"=r" (b->b)

99 :"" (b->a),"1" (b->b));

100 break;

101 case ROUND_DOWN:

102 if ((a->exponent & 0x8000) && (a->b & 0xff))

103 __asm__("addl $1,%0 ; adcl $0,%1"

104 :"=r" (b->a),"=r" (b->b)

105 :"" (b->a),"1" (b->b));

106 break;

107 case ROUND_UP:

108 if (!(a->exponent & 0x8000) && (a->b & 0xff))

109 __asm__("addl $1,%0 ; adcl $0,%1"

110 :"=r" (b->a),"=r" (b->b)

111 :"" (b->a),"1" (b->b));

112 break;

113 }

114 }

115

// ��ʱʵ��ת��ʱ��ʽ��

// ��ʱ��Ҳ��10�ֽڱ�ʾ��е�8�ֽ��޷��ֵ��2�ֽڱ�ʾָ��ֵ�ͷ��λ��

// ��2�ֽ��ЧλΪ1��ʾ�Ǹ��λ0��ʾ��

116 void real_to_int(const temp_real * a, temp_int * b)

117 {

118 int shift = 16383 + 63 - (a->exponent & 0x7fff);

119 unsigned long underflow;

120

121 b->a = b->b = underflow = 0;

122 b->sign = (a->exponent < 0);

123 if (shift < 0) {

124 set_OE();

125 return;

126 }

127 if (shift < 32) {

128 b->b = a->b; b->a = a->a;

129 } else if (shift < 64) {

130 b->a = a->b; underflow = a->a;

131 shift -= 32;

132 } else if (shift < 96) {

133 underflow = a->b;

134 shift -= 64;

135 } else

136 return;

137 __asm__("shrdl %2,%1,%0"

138 :"=r" (underflow),"=r" (b->a)

139 :"c" ((char) shift),"" (underflow),"1" (b->a));

140 __asm__("shrdl %2,%1,%0"

141 :"=r" (b->a),"=r" (b->b)

142 :"c" ((char) shift),"" (b->a),"1" (b->b));

143 __asm__("shrl %1,%0"

144 :"=r" (b->b)

145 :"c" ((char) shift),"" (b->b));

146 switch (ROUNDING) {

147 case ROUND_NEAREST:

148 __asm__("addl %4,%5 ; adcl $0,%0 ; adcl $0,%1"

149 :"=r" (b->a),"=r" (b->b)

150 :"" (b->a),"1" (b->b)

151 ,"r" (0x7fffffff + (b->a & 1))

152 ,"m" (*&underflow));

153 break;

154 case ROUND_UP:

155 if (!b->sign && underflow)

156 __asm__("addl $1,%0 ; adcl $0,%1"

157 :"=r" (b->a),"=r" (b->b)

158 :"" (b->a),"1" (b->b));

159 break;

160 case ROUND_DOWN:

161 if (b->sign && underflow)

162 __asm__("addl $1,%0 ; adcl $0,%1"

163 :"=r" (b->a),"=r" (b->b)

164 :"" (b->a),"1" (b->b));

165 break;

166 }

167 }

168

// ��ʱ��ת��ʱʵ��ʽ��

169 void int_to_real(const temp_int * a, temp_real * b)

170 {

// ��ԭֵ��ת��ʱʵ��ʱָ��Ҫ��ƫ��16383�⣬��Ҫ��63��

// ��ʾ��Ч��Ҫ��2��63�η��ֵ��

171 b->a = a->a;

172 b->b = a->b;

173 if (b->a || b->b)

174 b->exponent = 16383 + 63 + (a->sign? 0x8000:0);

175 else {

176 b->exponent = 0;

177 return;

178 }

// �Ը�ʽת��ʱʵ��й�񻯴��Ч��Чλ��0��

179 while (b->b >= 0) {

180 b->exponent--;

181 __asm__("addl %0,%0 ; adcl %1,%1"

182 :"=r" (b->a),"=r" (b->b)

183 :"" (b->a),"1" (b->b));

184 }

185 }

186