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refactor using subroutines
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@keiravillekode
keiravillekode committed Dec 25, 2024
1 parent ece06b7 commit 0ff16c6
Showing 1 changed file with 134 additions and 105 deletions.
239 changes: 134 additions & 105 deletions exercises/practice/meetup/.meta/example.s
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Original file line number Diff line number Diff line change
Expand Up @@ -14,23 +14,26 @@
.equ SUNDAY, 7

.data

/* offset from end February for the start of the specified month */
offset_array:
.hword -1
.hword -1
.hword -1
.hword 2 /* March */
.hword 33
.hword 63
.hword 94
.hword 124
.hword 155
.hword 186
.hword 216
.hword 247
.hword 277
.hword 308
.hword 339 /* February */

.hword 307
.hword 338
.hword 1 /* March */
.hword 32
.hword 62
.hword 93
.hword 123
.hword 154
.hword 185
.hword 215
.hword 246
.hword 276
.hword 307
.hword 338 /* February */

/* day in month for last day in specified week */
week_array:
.byte -1
.byte 7 /* first */
Expand All @@ -42,119 +45,145 @@ week_array:
.text
.globl meetup

/* extern void meetup(char *buffer, int year, int month, week_t week, dayofweek_t dayofweek); */
meetup:
adrp x5, offset_array
add x5, x5, :lo12:offset_array

mov w7, w1 /* adjusted year */
mov w8, w2 /* adjusted month */
cmp w2, #2
bgt .find_offset

sub w7, w7, #1
add w8, w8, #12 /* Consider January and February to be the 13th and 14th months of previous year */

.find_offset:
lsl w8, w8, #1
ldrh w9, [x5, x8] /* offset */
cmp w3, LAST
beq .last

adrp x6, week_array
add x6, x6, :lo12:week_array
ldrb w3, [x6, x3] /* day in month at end of requested week */

.total:
mov w5, w7 /* adjusted year */

lsr w7, w7, #2 /* adjusted year / 4 */
add w5, w5, w7

mov w10, #25
udiv w7, w7, w10 /* adjusted year / 100 */
sub w5, w5, w7

lsr w7, w7, #2 /* adjusted year / 400 */
add w5, w5, w7
/* void print_date(char *buffer, int year, int month, int day); */
print_date:
mov w9, #'-'
mov w10, 10 /* divisor */

add w5, w5, w9 /* add offset */
add w5, w5, w3 /* add day in month at end of requested week */
mov w10, #7
udiv w12, w5, w10 /* quotient */
msub w13, w12, w10, w5 /* remainder */

add w6, w3, w4
sub w6, w6, w13
cmp w6, w3
ble .write

sub w6, w6, #7

.write:
mov w10, #'-'
strb w10, [x0, #4]
strb w10, [x0, #7]
strb wzr, [x0, #10]

mov w10, 10 /* divisor */

mov w11, w1 /* year */
udiv w12, w11, w10 /* quotient */
msub w13, w12, w10, w11 /* remainder */
mov w11, w12
udiv w11, w1, w10 /* quotient */
msub w13, w11, w10, w1 /* remainder (year) */
add w13, w13, #'0'
strb w13, [x0, #3]

udiv w12, w11, w10 /* quotient */
msub w13, w12, w10, w11 /* remainder */
mov w11, w12
msub w13, w12, w10, w11 /* remainder (decade) */
add w13, w13, #'0'
strb w13, [x0, #2]

udiv w12, w11, w10 /* quotient */
msub w13, w12, w10, w11 /* remainder */
udiv w11, w12, w10 /* quotient */
msub w13, w11, w10, w12 /* remainder (century) */
add w13, w13, #'0'
strb w13, [x0, #1]
add w11, w11, #'0'
strb w11, [x0]

add w12, w12, #'0'
strb w12, [x0]
strb w9, [x0, #4]

mov w11, w2 /* month */
udiv w12, w11, w10 /* quotient */
msub w13, w12, w10, w11 /* remainder */
udiv w11, w2, w10 /* quotient */
msub w13, w11, w10, w2 /* remainder (month) */
add w13, w13, #'0'
strb w13, [x0, #6]
add w11, w11, #'0'
strb w11, [x0, #5]

add w12, w12, #'0'
strb w12, [x0, #5]
strb w9, [x0, #7]

mov w11, w6 /* day in month */
udiv w12, w11, w10 /* quotient */
msub w13, w12, w10, w11 /* remainder */
udiv w11, w3, w10 /* quotient */
msub w13, w11, w10, w3 /* remainder (day) */
add w13, w13, #'0'
strb w13, [x0, #9]
add w11, w11, #'0'
strb w11, [x0, #8]

add w12, w12, #'0'
strb w12, [x0, #8]
strb wzr, [x0, #10]
ret

.last:
/* int leap_year(void *unused, int year); */
leap_year:
mov w10, #100 /* divisor */
udiv w12, w1, w10 /* quotient, i.e. century */
msub w13, w12, w10, w1 /* remainder, i.e. year within century */
tst w13, w13 /* check if 0 */
csel w0, w12, w13, eq /* either century, or year within century */
tst w0, #3 /* check if multiple of 4 */
cset w0, eq
ret

/* int days_in_month(void *unused, int year, int month); */
days_in_month:
cmp w2, #2
beq .february

add w8, w8, #2
ldrh w10, [x5, x8] /* offset */
sub w3, w10, w9
b .total
adrp x9, offset_array
add x9, x9, :lo12:offset_array

lsl w10, w2, #1 /* month * sizeof(hword) */
ldrh w11, [x9, x10] /* days offset for required month */

add w10, w10, #2 /* (month + 1) * sizeof(hword) */
ldrh w0, [x9, x10] /* days offset for following month */

sub w0, w0, w11
ret

.february:
mov w10, #100 /* divisor */
udiv w12, w1, w10 /* quotient, i.e. century */
msub w13, w12, w10, w1 /* remainder, i.e. year within century */
tst w13, w13 /* check if 0 */
csel w3, w12, w13, eq /* either century, or year within century */
tst w3, #3 /* check if multiple of 4 */
cset w3, eq
add w3, w3, #28
b .total
mov x11, lr
bl leap_year
add w0, w0, #28
ret x11

/* int week_concludes(void *unused, int year, int month, week_t week); */
week_concludes:
cmp w3, LAST
beq days_in_month /* tail call */

adrp x9, week_array
add x9, x9, :lo12:week_array
ldrb w0, [x9, x3] /* day in month at end of requested week */
ret

/* dayofweek_t day_of_week(void *unused, int year, int month, int day); */
day_of_week:
mov w12, w2 /* month */
mov w11, w1 /* year */

add w10, w12, #12 /* Consider January and February to be the 13th and 14th months of */
sub w9, w11, #1 /* the previous year */
cmp w2, #2
csel w12, w12, w10, hi /* Conditionally adjust month */
csel w11, w11, w9, hi /* Conditionally adjust year */

lsl w12, w12, #1 /* (adjusted month) * sizeof(hword) */
adrp x9, offset_array
add x9, x9, :lo12:offset_array
ldrh w13, [x9, x12] /* days offset for required month */

mov w0, w11 /* adjusted year */

lsr w11, w11, #2 /* adjusted year / 4 */
add w0, w0, w11

mov w9, #25
udiv w11, w11, w9 /* adjusted year / 100 */
sub w0, w0, w11

lsr w11, w11, #2 /* adjusted year / 400 */
add w0, w0, w11

add w0, w0, w13 /* add offset */
add w0, w0, w3 /* add day in month */

mov w9, #7
udiv w10, w0, w9 /* quotient */
msub w0, w10, w9, w0 /* remainder */
add w0, w0, #1 /* day of week, in range 1..7 */
ret

/* extern void meetup(char *buffer, int year, int month, week_t week, dayofweek_t dayofweek); */
meetup:
mov x14, x0 /* buffer */
mov x15, lr /* return address */
bl week_concludes

mov w3, w0 /* day of month when week concludes */
bl day_of_week

sub w0, w4, w0 /* delta: requested day of week minus current day of week */
sub w9, w0, #7
cmp w0, wzr
csel w0, w0, w9, le /* if delta was positive, subtract 7 */
add w3, w3, w0 /* required day of month */
mov x0, x14 /* buffer */
bl print_date

ret x15

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