Chapter 19
- We can see that from the hexadecimal displays of the contents of
w19andw20that the fractional part is in the low-order four bits of the register and the integral part in the high-order 28 bits.(gdb) b 28 Breakpoint 1 at 0x7f8: file add_lengths.s, line 28. (gdb) r Starting program: /home/bob/add_lengths/add_lengths [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/aarch64-linux-gnu/libthread_db.so.1". Enter length (inches and 1/16s) Inches: 12 Sixteenths: 13 Enter length (inches and 1/16s) Inches: 4 Sixteenths: 15 Sum = Breakpoint 1, main () at add_lengths.s:28 28 add w0, w20, w19 // Add lengths (gdb) i r w19 w20 w19 0xcd 205 w20 0x4f 79 (gdb) - The decimal displays of the contents of
w19andw20show the scaled values of the numbers we entered. Since these are decimal values, the integral and fractional parts are not aligned to bit positions in the register.(gdb) b 28 Breakpoint 1 at 0x7f8: file add_money.s, line 28. (gdb) r Starting program: /home/bob/text_listings/add_money/add_money [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/aarch64-linux-gnu/libthread_db.so.1". Enter amount (use same sign for dollars and cents) Dollars: 1 Cents: 45 Enter amount (use same sign for dollars and cents) Dollars: 2 Cents: 67 Sum = Breakpoint 1, main () at add_money.s:28 28 add w0, w19, w20 // Add values (gdb) i r w19 w20 w19 0x91 145 w20 0x10b 267 (gdb) - The scaled value of 214743647 + 1 is 214743648, which is a negative number is 32 bits.
Enter amount (use same sign for dollars and cents) Dollars: 21474836 Cents: 47 Enter amount (use same sign for dollars and cents) Dollars: 0 Cents: 01 Sum = -$21474836.48 - My solution does not indicate when the sum goes to the next day. It just shoes an hour value greater than 24.
// Add two time values. .arch armv8-a // Stack frame .equ save1920, 16 .equ FRAME, 32 // Constant data .section .rodata .align 3 start_time: .string "Starting time\n" delta_time: .string "Duration time\n" end_time: .string "Ends at " // Code .text .align 2 .global main .type main, %function main: stp fp, lr, [sp, -FRAME]! // Create stack frame mov fp, sp // Set our frame pointer stp x19, x20, [sp, save1920] // For local vars adr x0, start_time // Ask for starting time bl write_str bl get_time mov w19, w0 // Start time adr x0, delta_time // Ask for duration time bl write_str bl get_time mov w20, w0 // Delta time adr x0, end_time // Ending message bl write_str add w0, w19, w20 // Add values bl display_time // Show ending time mov w0, '\n' // Finish formatting bl write_char mov w0, wzr // Return 0 ldp x19, x20, [sp, save1920] // Restore for caller ldp fp, lr, [sp], FRAME // Delete stack frame ret // Back to caller// Get hours, minute, and seconds from the keyboard. // Calling sequence // Return integer amount as seconds. .arch armv8-a // Stack frame .equ save19, 16 .equ FRAME, 32 # Constant data .section .rodata .align 3 hours: .string " Hours: " minutes: .string " Minutes: " seconds: .string " Seconds: " // Code .text .align 2 .global get_time .type get_time, %function get_time: stp fp, lr, [sp, -FRAME]! // Create stack frame mov fp, sp // Set our frame pointer str x19, [sp, save19] // For local var adr x0, hours // Ask for hours bl write_str bl get_uint // Hours mov w1, 3600 // 3600 seconds per hour mul w19, w0, w1 // Scale adr x0, minutes // Ask for minutes bl write_str bl get_uint // Minutes mov w1, 60 // 60 seconds per minute mul w0, w0, w1 // Scale add w19, w19, w0 // Add scaled minutes adr x0, seconds // Ask for seconds bl write_str bl get_uint // Seconds add w0, w19, w0 // Add seconds ldr x19, [sp, save19] // Restore for caller ldp fp, lr, [sp], FRAME // Delete stack frame ret // Back to caller// Display hours, minutes, and seconds. .arch armv8-a // Calling sequence // w0 <- value in seconds // Return 0. // Stack frame .equ save1920, 16 .equ FRAME, 32 # Constant data .section .rodata .align 3 // Code .text .align 2 .global display_time .type display_time, %function display_time: stp fp, lr, [sp, -FRAME]! // Create stack frame mov fp, sp // Set our frame pointer stp x19, x20, [sp, save1920] // For local vars mov w1, 3600 // 360 seconds per hour udiv w20, w0, w1 // Hours msub w19, w20, w1, w0 // Leaving seconds mov w0, w20 // Hours bl put_uint mov w0, ':' // Some formatting bl write_char mov w1, 60 // 60 seconds per minute udiv w20, w19, w1 // Minutes msub w19, w20, w1, w19 // Leaving seconds mov w0, w20 // Minutes bl put_uint mov w0, ':' // Some formatting bl write_char mov w0, w19 // Seconds bl put_uint mov w0, wzr // Return 0 ldp x19, x29, [sp, save1920] // Restore for caller ldp fp, lr, [sp], FRAME // Delete stack frame ret // Back to caller - Use doubles.
// Test the addition associativity of doubles. #include <stdio.h> #include <math.h> int main() { double x, y, z, sum1, sum2; printf("Enter a number: "); scanf("%lf", &x); printf("Enter a number: "); scanf("%lf", &y); printf("Enter a number: "); scanf("%lf", &z); sum1 = x + y; sum1 += z; /* sum1 = (x + y) + z */ sum2 = y + z; sum2 += x; /* sum2 = x + (y + z) */ if (sum1 == sum2) printf("%lf is the same as %lf\n", sum1, sum2); else printf("%lf is not the same as %lf\n", sum1, sum2); return 0; }Two runs of this program gave the following results:
bob@rpi5:~/chapter_19/your_turn/three_doubles_C $ ./three_doubles Enter a number: 10.1 Enter a number: 20.1 Enter a number: 30.1 60.300000 is the same as 60.300000 bob@rpi5:~/chapter_19/your_turn/three_doubles_C $ ./three_doubles Enter a number: 100.1 Enter a number: 200.1 Enter a number: 300.1 600.300000 is not the same as 600.300000We can conclude that addition of doubles is not associative.