shave some cycles off 16-bit squaring with shift instead of add

also fix the comments about how many cycles shift takes

Makefile

@@ -2,11 +2,8 @@
 
 all : mandel.xex
 
-mandel.xex : mandel.o mandel-core.o tables.o atari-xex.cfg
-	ld65 -C ./atari-xex.cfg --mapfile mandel.map -o $@ mandel.o mandel-core.o tables.o atari.lib
-
-mandel.s : mandel.c mandel.h
-	cc65 -o $@ mandel.c
+mandel.xex : mandel.o tables.o atari-asm-xex.cfg
+	ld65 -C ./atari-asm-xex.cfg -o $@ mandel.o tables.o
 
 %.o : %.s
 	ca65 -o $@ $<
@@ -16,7 +13,6 @@ tables.s : tables.js
 
 clean :
 	rm -f tables.s
-	rm -f mandel.s
 	rm -f *.o
 	rm -f *.xex
-	rm -f mandel.map
+

atari-xex.cfg

@@ -1,69 +0,0 @@
-# Sample linker configuration for C programs using the Atari binary file support.
-# Use with: cl65 -tatari -Catari-xex.cfg prog.c -o prog.xex
-FEATURES {
-    STARTADDRESS: default = $8000;
-}
-SYMBOLS {
-    __SYSTEM_CHECK__:    type = import;  # force inclusion of "system check" load chunk
-    __STACKSIZE__:       type = weak, value = $0800; # 2k stack
-    __STARTADDRESS__:    type = export, value = %S;
-    __RESERVED_MEMORY__: type = weak, value = $0000;
-    __SYSCHKHDR__:       type = export, value = 0; # Disable system check header
-    __SYSCHKTRL__:       type = export, value = 0; # Disable system check trailer
-    __TABLESEG_START__:    type = weak, value = $2E00 + $0300;
-    __TABLESEG_SIZE__:     type = weak, value = 6 * $100;
-    __BANKSY_START__:  type = weak, value = $4000;
-    __BANKSY_SIZE__:   type = weak, value = $4000;
-    __FRAMEBUFFER_START__: type = weak, value = $A000;
-}
-MEMORY {
-# Note -- $80 and $81 (LOMEM) appear to be reserved in ZP.
-    ZP:         file = "", define = yes, start = $0082, size = $007E;
-# "system check" load chunk
-    SYSCHKCHNK: file = %O,               start = $2E00, size = $0300;
-# Note $a000-$bfff is against the BASIC cartridge, may require booting with OPTION.
-    TABLES:     file = %O, define = yes, start = __TABLESEG_START__, size = __TABLESEG_SIZE__;
-# We reserve $4000-7fff for the bank-switch window.
-# In theory we could keep data and code here that we only use on 48k/64k systems.
-    BANKSWITCH: file = "", define = yes, start = __BANKSY_START__, size = __BANKSY_SIZE__;
-# "main program" load chunk
-    MAIN:       file = %O, define = yes, start = %S, size = __FRAMEBUFFER_START__ - __STACKSIZE__ - __RESERVED_MEMORY__ - %S;
-}
-FILES {
-    %O: format = atari;
-}
-FORMATS {
-    atari: runad = start,
-           initad = SYSCHKCHNK: __SYSTEM_CHECK__;
-}
-SEGMENTS {
-    ZEROPAGE:  load = ZP,         type = zp;
-    EXTZP:     load = ZP,         type = zp,                optional = yes;
-    SYSCHK:    load = SYSCHKCHNK, type = rw,  define = yes, optional = yes;
-    TABLES:    load = TABLES,     type = ro,  optional = yes, align = 256;
-    BANKSWICH: load = BANKSWITCH, type = ro,  optional = yes;
-    STARTUP:   load = MAIN,       type = ro,  define = yes;
-    LOWBSS:    load = MAIN,       type = rw,                optional = yes;  # not zero initialized
-    LOWCODE:   load = MAIN,       type = ro,  define = yes, optional = yes;
-    ONCE:      load = MAIN,       type = ro,                optional = yes;
-    CODE:      load = MAIN,       type = ro,  define = yes;
-    RODATA:    load = MAIN,       type = ro;
-    DATA:      load = MAIN,       type = rw;
-    INIT:      load = MAIN,       type = rw,                optional = yes;
-    BSS:       load = MAIN,       type = bss, define = yes;
-}
-FEATURES {
-    CONDES: type    = constructor,
-            label   = __CONSTRUCTOR_TABLE__,
-            count   = __CONSTRUCTOR_COUNT__,
-            segment = ONCE;
-    CONDES: type    = destructor,
-            label   = __DESTRUCTOR_TABLE__,
-            count   = __DESTRUCTOR_COUNT__,
-            segment = RODATA;
-    CONDES: type    = interruptor,
-            label   = __INTERRUPTOR_TABLE__,
-            count   = __INTERRUPTOR_COUNT__,
-            segment = RODATA,
-            import  = __CALLIRQ__;
-}

mandel.c

@@ -1,15 +0,0 @@
-/**
- * The UI and I/O wrapper for the Mandelbrot runner, in C.
- *
- * For the moment *all* logic is in mandel-core.s, I'm just
- * trying to get this to run within a cc65 environment.
- * Eventually just the inner loop fun will live in there.
- */
-
-#include <stdlib.h>
-#include <stdio.h>
-#include "mandel.h"
-
-void main(void) {
-    mandel_start();
-}

mandel.h

@@ -1,4 +0,0 @@
-#include <inttypes.h>
-
-// From mandel-core.s:
-extern void mandel_start(void);

readme.md

@@ -18,7 +18,7 @@ Enjoy! I'll probably work on this off and on for the next few weeks until I've g
 
 ## Current state
 
-Basic rendering is functional, with interactive zoom/pan (+/-/arrows) and 6 preset viewports via the number keys.
+Basic rendering is functional, with interactive zoom/pan (+/-/arrows) and 4 preset viewports via the number keys.
 
 The 16-bit signed integer multiplication takes two 16-bit inputs and emits one 32-bit output in the zero page, using the Atari OS ROM's floating point registers as workspaces. Inputs are clobbered.
 
@@ -27,7 +27,7 @@ The 16-bit signed integer multiplication takes two 16-bit inputs and emits one 3
 * when expanded RAM is available as on 130XE, a 64KB 8-bit multiplication table accelerates the remaining multiplications
 * without expanded RAM, a table of half-squares is used to implement the algorithm from https://everything2.com/title/Fast+6502+multiplication
 
-The mandelbrot calculations are done using 3.13-precision fixed point numbers with 6.26-precision intermediates.
+The mandelbrot calculations are done using 4.12-precision fixed point numbers. It may be possible to squish this down to 3.13.
 
 Iterations are capped at 255.
 
@@ -47,4 +47,4 @@ Currently produces a `.xex` executable, which can be booted up in common Atari e
 
 ## Todo
 
-See ideas in `todo.md`.
+See ideas in `todo.md`.

tables.js

@@ -11,40 +11,19 @@ function db(func) {
     return lines.join('\n');
 }
 
-let squares = [];
-for (let i = 0; i < 512; i++) {
-    squares.push(Math.trunc((i * i + 1) / 2));
-}
-
 console.log(
 `.segment "TABLES"
 
-.export mul_lobyte256
-.export mul_hibyte256
-.export mul_hibyte512
-.export sqr_lobyte
-.export sqr_hibyte
+.export mul_lobyte
+.export mul_hibyte
 
-; (i * i + 1) / 2 for the multiplier
+; (i * i) / 2 for the multiplier
 .align 256
-mul_lobyte256:
-${db((i) => squares[i] & 0xff)}
+mul_lobyte:
+${db((i) => ((i * i) >> 1) & 0xff)}
 
 .align 256
-mul_hibyte256:
-${db((i) => (squares[i] >> 8) & 0xff)}
-
-.align 256
-mul_hibyte512:
-${db((i) => (squares[i + 256] >> 8) & 0xff)}
-
-; (i * i) for the plain squares
-.align 256
-sqr_lobyte:
-${db((i) => (i * i) & 0xff)}
-
-.align 256
-sqr_hibyte:
-${db((i) => ((i * i) >> 8) & 0xff)}
+mul_hibyte:
+${db((i) => ((i * i) >> 9) & 0xff)}
 
 `);

todo.md

@@ -1,17 +1,15 @@
 things to try:
 
-* fix status bar to show elapsed time, per-iter time, per-pixel iter count
-
-* 'turbo' mode disabling graphics in full or part
-
 * patch the entire expanded-ram imul8xe on top of imul8 to avoid the 3-cycle thunk penalty :D
 
-* maybe clean up the load/layout of the big mul table
-
-* consider alternate lookup tables in the top 16KB under ROM
+* try 3.13 fixed point instead of 4.12 for more precision
+  * can we get away without the extra bit?
 
 * y-axis mirror optimization
 
+* 'wide pixels' 2x and 4x for a fuller initial image in the tiered rendering
+  * maybe redo tiering to just 4x4, 2x2, 1x1?
+
 * extract viewport for display & re-input via keyboard
 
 * fujinet screenshot/viewport uploader