Ported libc time library

Includes:
- clock() - was done previously
- difftime()
- mktime()
- time()
- localtime()
- gmtime()
- asctime()
- ctime()

README.md

@@ -95,11 +95,11 @@ In the relevant: example, test or any other directory created at the same level.
 
 25/06/2023:
 
-- `scanf` and sscanf moved into standard library (libc)
+- `scanf` and `sscanf` moved into standard library (libc)
 
 30/06/2023:
 
-- bug in strncpy.src which used a ZDS pseudo op that is not implemented in fasmg assembler. Replaced by individual assembly instructions. This problem may occur in other libraries copied from ZDS. For the moment, just fixed in this one location.
+- bug in `strncpy.src` which used a ZDS pseudo op that is not implemented in fasmg assembler. Replaced by individual assembly instructions. This problem may occur in other libraries copied from ZDS. For the moment, just fixed in this one location.
 
 - C-runtime `crt0.src` updated to added back functionality previously removed as part of the proof of concept
 
@@ -135,7 +135,11 @@ In the relevant: example, test or any other directory created at the same level.
 
 - Corrected` lib/crt/fpftol.src` to remove ZDS pseudo op not supported by fasmg and removed other ZDS assembler features that are different in fasmg
 
-- Corrected lib/crt/fpultof.src to remover ZDS assembler directives that are different in fasmg
+- Corrected `lib/crt/fpultof.src` to remove ZDS assembler directives that are different in fasmg
+
+- Ported time functions: `difftime()`, `mktime()`, `time()`, `localtime()`, `gmtime()`, `asctime()`, `ctime()` 
+
+- Updated comments in `mos_api.h` to note that `getsysvar_rtc()` data is only updated when `mos_getrtc()` is called. This is taken account of in `time()`.
 
 ### To-Do:
 

include/mos_api.h

@@ -160,7 +160,7 @@ extern uint8_t  getsysvar_scrpixelIndex();
 extern uint8_t  getsysvar_vkeycode();
 extern uint8_t  getsysvar_vkeydown();
 extern uint8_t  getsysvar_vkeycount();
-extern volatile RTC_DATA* getsysvar_rtc();
+extern volatile RTC_DATA* getsysvar_rtc();  // mos_getrtc() needs to be called to update the values
 extern uint16_t getsysvar_keydelay();
 extern uint16_t getsysvar_keyrate();
 extern uint8_t  getsysvar_keyled();

include/time.h

@@ -0,0 +1,83 @@
+#ifndef _TIME_H
+#define _TIME_H
+
+#include <cdefs.h>
+
+#ifndef LOCALTIME_GMT_OFFSET
+#define LOCALTIME_GMT_OFFSET 0
+#endif
+
+#ifndef CLOCKS_PER_SEC
+#define CLOCKS_PER_SEC 100UL
+#endif
+
+/* Time Types
+
+Data Type: clock_t
+------------------
+clock_t is used to measure processor and CPU time. It may be an integer or a floating-point type.
+Its values are counts of clock ticks since some arbitrary event in the past. The number of clock ticks
+per second is system-specific.
+- On Agon it is an unsigned long & ticks are in centi-seconds. It is incremented by 2 by MOS in
+  the vertical blanking interrupt
+
+Data Type: time_t
+-----------------
+time_t is the simplest data type used to represent simple calendar time.
+
+In ISO C, time_t can be either an integer or a floating-point type, and the meaning of time_t values
+is not specified. The only things a strictly conforming program can do with time_t values are:
+pass them to difftime to get the elapsed time between two simple calendar times (see Calculating Elapsed
+Time), and pass them to the functions that convert them to broken-down time (see Broken-down Time).
+
+On POSIX-conformant systems, time_t is an integer type and its values represent the number of seconds
+elapsed since the epoch, which is 00:00:00 on January 1, 1970, Coordinated Universal Time.
+
+The GNU C Library additionally guarantees that time_t is a signed type, and that all of its functions
+operate correctly on negative time_t values, which are interpreted as times before the epoch.
+- On Agon it is an unsigned long, representing the numer of seconds elapsed since the the epoch
+
+Data Type: struct tm
+--------------------
+struct tm is a broken-down time is a binary representation of calendar time separated into year, month,
+day, and so on. Broken-down time values are not useful for calculations, but they are useful for printing
+human readable time information (see details in the struct definition below.
+*/
+
+typedef unsigned long time_t;
+typedef unsigned long clock_t;
+
+struct tm {
+   int tm_sec;          // normally 0-59, can be 60 for leap-second
+   int tm_min;          // 0-59
+   int tm_hour;         // 0-23
+   int tm_mday;         // 1-31 (note starts at 1, not 0)
+   int tm_mon;          // 0-11
+   int tm_year;         // Number of full calendar years since 1990
+   int tm_wday;         // 0-6 (0=Sunday)
+   int tm_yday;         // 0-365
+   int tm_isdst;        // Daylight saving flag (+ve if in effect, 0 if not, -ve if unknown)
+};
+
+__BEGIN_DECLS
+
+clock_t clock(void);
+
+double difftime(time_t time1, time_t time0)
+    __attribute__((__const__));
+
+time_t mktime(struct tm *tmp);
+
+time_t time(time_t *timer);
+
+struct tm *localtime(const time_t *timer);
+
+struct tm *gmtime(const time_t *timer);
+
+char *asctime(const struct tm *tmp);
+
+char *ctime(const time_t *timer);
+
+__END_DECLS
+
+#endif /* _TIME_H */

lib/libc/gmtime.c.src

@@ -0,0 +1,224 @@
+	section	.text,"ax",@progbits
+	assume	adl = 1
+	section	.text,"ax",@progbits
+	public	_gmtime
+_gmtime:
+	ld	hl, -10
+	call	__frameset
+	ld	iy, (ix + 6)
+	ld	bc, 0
+	xor	a, a
+	lea	hl, iy
+	ld	hl, (hl)
+	ld	e, (iy + 3)
+	ld	iy, 70
+	ld	(_gmtime.tm2), bc
+	ld	(_gmtime.tm2+3), bc
+	ld	(_gmtime.tm2+6), bc
+	inc	bc
+	ld	(_gmtime.tm2+9), bc
+	dec	bc
+	ld	(_gmtime.tm2+12), bc
+	ld	(_gmtime.tm2+15), iy
+	ld	(ix - 3), hl
+	ld	(ix - 4), e
+	ld	bc, 86400
+	call	__ldivu
+	ld.sis	de, 4
+	add.sis	hl, de
+	ld.sis	bc, 7
+	call	__sremu
+	ld	de, 0
+	ld	e, l
+	ld	d, h
+	ld	(_gmtime.tm2+18), de
+	scf
+	sbc	hl, hl
+	ld	(_gmtime.tm2+24), hl
+BB0_1:
+	push	iy
+	call	_istmleap
+	pop	hl
+	bit	0, a
+	ld	bc, -1932032
+	jr	nz, BB0_3
+	ld	bc, -2018432
+BB0_3:
+	bit	0, a
+	ld	d, 0
+	ld	iy, 86400
+	ld	hl, (ix - 3)
+	ld	e, (ix - 4)
+	ld	a, 1
+	call	__lcmpu
+	jr	c, BB0_5
+	call	__lsub
+	ld	(ix - 3), hl
+	ld	(ix - 4), e
+	ld	iy, (_gmtime.tm2+15)
+	inc	iy
+	ld	(_gmtime.tm2+15), iy
+	jr	BB0_1
+BB0_5:
+	lea	bc, iy
+	ld	a, d
+	call	__ldivu
+	ld	(_gmtime.tm2+21), hl
+	ld	hl, (_gmtime.tm2+15)
+	push	hl
+	call	_istmleap
+	pop	hl
+	bit	0, a
+	jr	z, BB0_7
+	ld	a, 29
+	ld	(_gmtime.dpm+1), a
+BB0_7:
+	ld	bc, (_gmtime.tm2+12)
+	ld	d, 0
+	ld	a, d
+	ld	hl, _gmtime.dpm
+BB0_8:
+	ld	iy, 0
+	ld	(ix - 7), bc
+	add	hl, bc
+	push	af
+	ld	a, (hl)
+	ld	iyl, a
+	pop	af
+	ld	e, iyh
+	lea	hl, iy
+	ld	bc, 86400
+	ld	d, a
+	call	__lmulu
+	push	hl
+	pop	bc
+	ld	a, e
+	ld	hl, (ix - 3)
+	ld	e, (ix - 4)
+	call	__lcmpu
+	jr	c, BB0_10
+	ld	e, 0
+	ld	hl, (ix - 7)
+	push	hl
+	pop	bc
+	inc	bc
+	ld	(ix - 10), bc
+	inc	hl
+	ld	(_gmtime.tm2+12), hl
+	lea	hl, iy
+	ld	bc, -86400
+	ld	a, -1
+	call	__lmulu
+	ld	bc, (ix - 3)
+	ld	a, (ix - 4)
+	call	__ladd
+	ld	(ix - 3), hl
+	ld	(ix - 4), e
+	ld	bc, (ix - 10)
+	ld	hl, _gmtime.dpm
+	ld	a, d
+	jr	BB0_8
+BB0_10:
+	ld	a, 28
+	ld	(_gmtime.dpm+1), a
+	ld	iy, (_gmtime.tm2+9)
+	inc	iy
+	ld	bc, (ix - 3)
+	ld	a, (ix - 4)
+BB0_11:
+	ld	hl, 86399
+	ld	e, d
+	call	__lcmpu
+	jr	nc, BB0_13
+	push	bc
+	pop	hl
+	ld	e, a
+	ld	bc, -86400
+	ld	a, -1
+	call	__ladd
+	push	hl
+	pop	bc
+	ld	a, e
+	ld	(_gmtime.tm2+9), iy
+	inc	iy
+	jr	BB0_11
+BB0_13:
+	ld	iy, (_gmtime.tm2+6)
+BB0_14:
+	inc	iy
+	ld	hl, 3599
+	ld	e, d
+	call	__lcmpu
+	jr	nc, BB0_16
+	push	bc
+	pop	hl
+	ld	e, a
+	ld	bc, -3600
+	ld	a, -1
+	call	__ladd
+	push	hl
+	pop	bc
+	ld	a, e
+	ld	(_gmtime.tm2+6), iy
+	jr	BB0_14
+BB0_16:
+	ld	iy, (_gmtime.tm2+3)
+BB0_17:
+	inc	iy
+	ld	hl, 59
+	ld	e, d
+	call	__lcmpu
+	jr	nc, BB0_19
+	push	bc
+	pop	hl
+	ld	e, a
+	ld	bc, -60
+	ld	a, b
+	call	__ladd
+	push	hl
+	pop	bc
+	ld	a, e
+	ld	(_gmtime.tm2+3), iy
+	jr	BB0_17
+BB0_19:
+	ld	(_gmtime.tm2), bc
+	ld	hl, _gmtime.tm2
+	ld	sp, ix
+	pop	ix
+	ret
+	section	.text,"ax",@progbits
+
+	section	.text,"ax",@progbits
+	private	_istmleap
+_istmleap:
+	call	__frameset0
+	ld	hl, (ix + 6)
+	ld	de, 1900
+	add	hl, de
+	ld	(ix + 6), hl
+	pop	ix
+	jp	___isleap
+	section	.text,"ax",@progbits
+
+	section	.data,"aw",@progbits
+	private	_gmtime.dpm
+_gmtime.dpm:
+	db	""
+
+	section	.bss,"aw",@nobits
+	private	_gmtime.tm2
+_gmtime.tm2:
+	rb	27
+
+	ident	"clang version 15.0.0 (https://github.com/jacobly0/llvm-project 6c61664110f888c0285ae4c48b150c9a7a4361bb)"
+	extern	__ldivu
+	extern	__Unwind_SjLj_Register
+	extern	__Unwind_SjLj_Unregister
+	extern	__frameset
+	extern	__sremu
+	extern	__lmulu
+	extern	__lsub
+	extern	__lcmpu
+	extern	__frameset0
+	extern	__ladd
+	extern	___isleap

lib/libc/localtime.c.src

@@ -0,0 +1,24 @@
+	section	.text,"ax",@progbits
+	assume	adl = 1
+	section	.text,"ax",@progbits
+	public	_localtime
+_localtime:
+	ld	hl, -4
+	call	__frameset
+	ld	iy, (ix + 6)
+	ld	hl, (iy)
+	ld	a, (iy + 3)
+	ld	(ix - 4), hl
+	ld	(ix - 1), a
+	pea	ix - 4
+	call	_gmtime
+	ld	sp, ix
+	pop	ix
+	ret
+	section	.text,"ax",@progbits
+
+	ident	"clang version 15.0.0 (https://github.com/jacobly0/llvm-project 6c61664110f888c0285ae4c48b150c9a7a4361bb)"
+	extern	__Unwind_SjLj_Register
+	extern	__Unwind_SjLj_Unregister
+	extern	__frameset
+	extern	_gmtime