Page 277 - ARM 64 Bit Assembly Language

266 Chapter 8

104 }
105
106 /* Print a signed fixed point number with the given number of
107 bits in the fractional part. NOTE: frac_bits must be between
108 0 and 31 for this function to work properly.
109 */
110 #define MAX_DIGITS 8
111 void printS( int num, int frac_bits )
112 {
113 unsigned int mask = (1 << frac_bits) - 1;
114 unsigned int fracpart;
115 int intpart;
116 int count = 0;
117 int frac_digits[MAX_DIGITS+1];
118
119 if(num < 0)
120 {
121 printf("-");
122 num = -num;
123 }
124 else
125 printf(" ");
126 /* Remove the integer part and keep the fraction part */
127 fracpart = num & mask;
128 intpart = num>>frac_bits;
129
130 /* Print all of the digits in the fraction part into frac_digits.*/
131 for(count=0;count<MAX_DIGITS+1;count++)
132 {
133 fracpart *= 10;
134 frac_digits[count] = fracpart >> frac_bits;
135 fracpart &= mask ;
136 }
137
138 /* Round the fractional part */
139 frac_digits[MAX_DIGITS] += 5;
140 intpart += roundit(frac_digits,MAX_DIGITS);
141 /* Print the integer part (with the sign, if it is negative) */
142 printf("%d.",intpart);
143 /* Print the fractional digits */
144 for(count=0;count<MAX_DIGITS;count++)
145 printf("%d",frac_digits[count]);
146 }

These functions are not meant to be particularly efficient, but are given as examples of the
types of functions that would be needed for input and output of fixed point numbers. Another
way to approach fixed point I/O would be to provide only functions to convert fixed point val-
ues of various sizes to and from C strings, then use scanf and printf to read and write the