day 8

Makefile

@@ -14,13 +14,13 @@ LFLAGS = -Ttext=C475000 -static -nostdlib -no-pie
 
 all: $(BINS)
 
-%.elf: %.o start.o | %.c lib.h $(MUSLOBJS)
+%.elf: %.o start.o | %.c $(MUSLOBJS)
 	ld -o $@ $(LFLAGS) start.o $< $(MUSLOBJS)
 
 start.o: start.s
 	nasm -f elf64 -o $@ $<
 
-%.o: %.c
+%.o: %.c | lib.h
 	gcc-tree -o $@ $(CFLAGS) $<
 
 clean:

day0.h

@@ -3,46 +3,45 @@
 #define DBG 0
 
 static
-unsigned char input[] = {
+ch input[] = {
 #embed "day0_input.txt"
 };
 
 static
-unsigned char test[] = {
+ch test[] = {
 #embed "day0_test.txt"
 };
 
+alignas(0x40) static
+struct {
+    line padstart[4];
+    struct { ch *s; num _extra[7]; };
+    union { line l; struct { ch s[16]; num n; }; } result;
+    line padend;
+} m;
+static_assert(offsetof(typeof(m),result) % 64 == 0);
+static_assert(offsetof(typeof(m),padend) % 64 == 0);
 
 static
-unsigned long do_part1(size_t file_len, unsigned char file[file_len]) {
-    unsigned char *s = file;
-    unsigned long result = 0;
+num do_part1(size_t file_len, ch file[file_len]) {
+    m = (typeof(m)){ };
+    m.s = file;
+    m.result.n = 0;
 
 #if DBG
     print("\n");
 #endif
 
 do {
-    s++;
-} while (s != &file[file_len]);
+    m.s++;
+} while (m.s != &file[file_len]);
 
-    return result;
+    return m.result.n;
 }
 
 static
-unsigned long do_part2(size_t file_len, unsigned char file[file_len]) {
-    unsigned char *s = file;
-    unsigned long result = 0;
-
-#if DBG
-    print("\n");
-#endif
-
-do {
-    s++;
-} while (s != &file[file_len]);
-
-    return result;
+num do_part2(size_t file_len, ch file[file_len]) {
+    return 0;
 }
 
 #define RUN_TEST1 1
@@ -56,7 +55,7 @@ do {
 void run() {
 #if RUN_TEST1
     print("PART 1 TEST: ");
-    if (unsigned long v = do_part1(countof(test), test); v != TEST1_EXPECT) {
+    if (num v = do_part1(countof(test), test); v != TEST1_EXPECT) {
         print("FAILED (got ");
         printd(v);
         print(", expected " xstr(TEST1_EXPECT) ")\n");
@@ -73,7 +72,7 @@ void run() {
 
 #if RUN_TEST2
     print("PART 2 TEST: ");
-    if (unsigned long v = do_part2(countof(test), test); v != TEST2_EXPECT) {
+    if (num v = do_part2(countof(test), test); v != TEST2_EXPECT) {
         print("FAILED (got ");
         printd(v);
         print(", expected " xstr(TEST2_EXPECT) ")\n");

day6.c

@@ -0,0 +1,228 @@
+#include "lib.h"
+
+#define DBG 0
+
+static
+ch input[] = {
+#embed "day6_input.txt"
+};
+
+static
+ch test[] = {
+#embed "day6_test.txt"
+};
+
+static
+num do_part1(size_t file_len, ch file[file_len]) {
+    ch *s = file;
+    num result = 0;
+
+    s = memchr(s, '\n', file_len);
+    num stride = s - file;
+
+    s = file;
+    while (*s != '+' && *s != '*') s += stride;
+    num heightb = (s - file);
+    num height  = (s - file) / stride;
+    ch *op = s;
+
+    // constructing a pointer more than 1 past the end of an array
+    // is UB, sadly, so we'll use offsets
+    num op_off = op - file;
+    s = file;
+    do {
+        num ledge_off = op_off - heightb;
+        if (s[op_off] == '+') {
+            num a = 0;
+            num rem = height;
+            do {
+                ch *t = s + ledge_off;
+                while (*t < '0') t++;
+                num b = grabnum(t, NULL);
+                a += b;
+                ledge_off += stride;
+                rem--;
+            } while (rem);
+            result += a;
+        } else if (s[op_off] == '*') {
+            num a = 1;
+            num rem = height;
+            do {
+                ch *t = s + ledge_off;
+                while (*t < '0') t++;
+                num b = grabnum(t, NULL);
+#if DBG
+                if (rem < height) { print("\t*\t"); }
+                printd(b);
+#endif
+                a *= b;
+                ledge_off += stride;
+                rem--;
+            } while (rem);
+            result += a;
+#if DBG
+            print("\t= "); printd(a); print("\n");
+#endif
+        }
+#if DBG
+        else {
+            print("INVALID OP\n");
+            exit_group(-1);
+        }
+#endif
+        op_off++;
+        while (op_off < file_len) {
+            if (s[op_off] == '+' || s[op_off] == '*')
+                break;
+            op_off++;
+        }
+    } while (op_off < file_len);
+
+    return result;
+}
+
+static
+num do_part2(size_t file_len, unsigned char file[file_len]) {
+    ch *s = file;
+    num result = 0;
+
+#if DBG
+    print("\n");
+#endif
+
+    s = memchr(s, '\n', file_len);
+    num stride = s - file;
+
+    s = file;
+    while (*s != '+' && *s != '*') s += stride;
+    num heightb = (s - file);
+    num height  = (s - file) / stride;
+    ch *op = s;
+
+#if DBG
+    print("STRIDE\t"); printd(stride); print("\n");
+    print("HEIGHT\t"); printd(height); print("\n");
+#endif
+
+    // constructing a pointer more than 1 past the end of an array
+    // is UB, sadly, so we'll use offsets
+    num fop_off = op - file;
+    num prev_op_off = fop_off + stride - 1;
+    s = file;
+    do {
+        // we don't need to do these in the same order as the example
+        // because both these operations are commutative.
+        // but you know what? we can anyway. for fun. and pretty output
+        num op_off = prev_op_off - 1;
+        while (s[op_off] != '+' && s[op_off] != '*' && s[op_off] != '\n')
+            op_off--;
+        num ledge_off = op_off - heightb;
+        num redge_off = (s[prev_op_off] == '\n' ? -1 : -2) + prev_op_off - heightb;
+        if (s[op_off] == '+') {
+            num a = 0;
+            num rem = redge_off - ledge_off + 1;
+            num frem = rem;
+            do {
+                num b = 0;
+                ch *t = s + redge_off;
+                for (num i = height; i; i--,t+=stride) {
+                    if (*t >= '0') {
+                        b *= 10;
+                        b += *t - '0';
+                    }
+                }
+#if DBG
+                if (rem < frem) { print("\t+\t"); }
+                printd(b);
+#endif
+                a += b;
+                redge_off--;
+                rem--;
+            } while (rem);
+            result += a;
+#if DBG
+            print("\t=\t"); printd(a); print("\n");
+#endif
+        } else if (s[op_off] == '*') {
+            num a = 1;
+            num rem = redge_off - ledge_off + 1;
+            num frem = rem;
+            do {
+                num b = 0;
+                ch *t = s + redge_off;
+                for (num i = height; i; i--,t+=stride) {
+                    if (*t >= '0') {
+                        b *= 10;
+                        b += *t - '0';
+                    }
+                }
+#if DBG
+                if (rem < frem) { print("\t*\t"); }
+                printd(b);
+#endif
+                a *= b;
+                redge_off--;
+                rem--;
+            } while (rem);
+            result += a;
+#if DBG
+            print("\t=\t"); printd(a); print("\n");
+#endif
+        }
+#if DBG
+        else {
+            print("INVALID OP\n");
+            exit_group(-1);
+        }
+#endif
+        prev_op_off = op_off;
+    } while (prev_op_off != fop_off);
+
+    return result;
+}
+
+#define RUN_TEST1 1
+#define RUN_PART1 1
+#define RUN_TEST2 1
+#define RUN_PART2 1
+
+#define TEST1_EXPECT 4277556
+#define TEST2_EXPECT 3263827
+
+void run() {
+#if RUN_TEST1
+    print("PART 1 TEST: ");
+    if (num v = do_part1(countof(test), test); v != TEST1_EXPECT) {
+        print("FAILED (got ");
+        printd(v);
+        print(", expected " xstr(TEST1_EXPECT) ")\n");
+    } else {
+        print("PASSED\n");
+    }
+#endif
+
+#if RUN_PART1
+    print("PART 1 RESULT: ");
+    printd(do_part1(countof(input), input));
+    print("\n");
+#endif
+
+#if RUN_TEST2
+    print("PART 2 TEST: ");
+    if (num v = do_part2(countof(test), test); v != TEST2_EXPECT) {
+        print("FAILED (got ");
+        printd(v);
+        print(", expected " xstr(TEST2_EXPECT) ")\n");
+    } else {
+        print("PASSED\n");
+    }
+#endif
+
+#if RUN_PART2
+    print("PART 2 RESULT: ");
+    printd(do_part2(countof(input), input));
+    print("\n");
+#endif
+
+    exit_group(0);
+}

day6pretty.c

@@ -0,0 +1,228 @@
+#include "lib.h"
+
+static
+ch input[] = {
+#embed "day6_input.txt"
+};
+
+static
+ch test[] = {
+#embed "day6_test.txt"
+};
+
+typedef struct { ch l[64]; } line;
+static_assert(sizeof(line) == 0x40);
+
+alignas(0x40) static
+struct {
+    line padstart[4];
+    struct { num pad[3]; num prev_op_off, op_off, ledge_off, redge_off, rem; };
+    union { line l; struct { ch s[16]; num op, pad0, pad1, v; }; } b;
+    union { line l; struct { ch s[16], pad0, sr[16], pad1; num v, vr; }; } a;
+    line padend;
+} m;
+static_assert(offsetof(typeof(m),b) % 64 == 0);
+static_assert(sizeof(m.b) == 64);
+static_assert(sizeof(m.a) == 64);
+static_assert(offsetof(typeof(m),padend) % 64 == 0);
+
+static
+num do_part1(size_t file_len, ch file[file_len]) {
+    ch *s = file;
+    m = (typeof(m)){ };
+
+    s = memchr(s, '\n', file_len);
+    const num stride = s - file;
+
+    s = file;
+    while (*s != '+' && *s != '*') s += stride;
+    const num heightb = (s - file);
+    const num height  = (s - file) / stride;
+    ch *const op = s;
+
+    // constructing a pointer more than 1 past the end of an array
+    // is UB, sadly, so we'll use offsets
+    m.op_off = op - file;
+    s = file;
+    do {
+        m.ledge_off = m.op_off - heightb;
+        if (s[m.op_off] == '+') {
+            m.a.v = 0;
+            m.rem = height;
+            m.b.op = '+' << 8;
+            snprintd(m.a.v, 16, m.a.s);
+            do {
+                ch *t = s + m.ledge_off;
+                while (*t < '0') t++;
+                m.b.v = grabnum(t, NULL);
+                snprintd(m.b.v, 16, m.b.s);
+                m.a.v += m.b.v;
+                snprintd(m.a.v, 16, m.a.s);
+                m.ledge_off += stride;
+                m.rem--;
+            } while (m.rem);
+            m.a.vr += m.a.v;
+            snprintd(m.a.vr, 16, m.a.sr);
+        } else if (s[m.op_off] == '*') {
+            m.a.v = 1;
+            m.rem = height;
+            m.b.op = '*' << 8;
+            snprintd(m.a.v, 16, m.a.s);
+            do {
+                ch *t = s + m.ledge_off;
+                while (*t < '0') t++;
+                m.b.v = grabnum(t, NULL);
+                snprintd(m.b.v, 16, m.b.s);
+                m.a.v *= m.b.v;
+                snprintd(m.a.v, 16, m.a.s);
+                m.ledge_off += stride;
+                m.rem--;
+            } while (m.rem);
+            m.a.vr += m.a.v;
+            snprintd(m.a.vr, 16, m.a.sr);
+        }
+        m.op_off++;
+        while (m.op_off < file_len) {
+            if (s[m.op_off] == '+' || s[m.op_off] == '*')
+                break;
+            m.op_off++;
+        }
+    } while (m.op_off < file_len);
+
+    return m.a.vr;
+}
+
+static
+num do_part2(size_t file_len, unsigned char file[file_len]) {
+    ch *s = file;
+    m = (typeof(m)){ };
+
+    s = memchr(s, '\n', file_len);
+    const num stride = s - file;
+
+    s = file;
+    while (*s != '+' && *s != '*') s += stride;
+    const num heightb = (s - file);
+    const num height  = (s - file) / stride;
+    ch *const op = s;
+
+    // constructing a pointer more than 1 past the end of an array
+    // is UB, sadly, so we'll use offsets
+    const num fop_off = op - file;
+    m.prev_op_off = fop_off + stride - 1;
+    s = file;
+    do {
+        // we don't need to do these in the same order as the example
+        // because both these operations are commutative.
+        // but you know what? we can anyway. for fun. and pretty output
+        {
+            num op_off = m.prev_op_off - 1;
+            while (s[op_off] != '+' && s[op_off] != '*' && s[op_off] != '\n')
+                op_off--;
+            m.op_off = op_off;
+        }
+        m.ledge_off = m.op_off - heightb;
+        m.redge_off = (s[m.prev_op_off] == '\n' ? -1 : -2) + m.prev_op_off - heightb;
+        if (s[m.op_off] == '+') {
+            m.a.v = 0;
+            m.rem = m.redge_off - m.ledge_off + 1;
+            const num frem = m.rem;
+
+            m.b.op = '+' << 8;
+            snprintd(m.a.v, 16, m.a.s);
+
+            do {
+                m.b.v = 0;
+                ch *t = s + m.redge_off;
+                for (num i = height; i; i--,t+=stride) {
+                    if (*t >= '0') {
+                        m.b.v *= 10;
+                        m.b.v += *t - '0';
+                    }
+                }
+                snprintd(m.b.v, 16, m.b.s);
+                m.a.v += m.b.v;
+                snprintd(m.a.v, 16, m.a.s);
+                m.redge_off--;
+                m.rem--;
+            } while (m.rem);
+            m.a.vr += m.a.v;
+            snprintd(m.a.vr, 16, m.a.sr);
+        } else if (s[m.op_off] == '*') {
+            m.a.v = 1;
+            m.rem = m.redge_off - m.ledge_off + 1;
+            const num frem = m.rem;
+
+            m.b.op = '*' << 8;
+            snprintd(m.a.v, 16, m.a.s);
+
+            do {
+                m.b.v = 0;
+                ch *t = s + m.redge_off;
+                for (num i = height; i; i--,t+=stride) {
+                    if (*t >= '0') {
+                        m.b.v *= 10;
+                        m.b.v += *t - '0';
+                    }
+                }
+                snprintd(m.b.v, 16, m.b.s);
+                m.a.v *= m.b.v;
+                snprintd(m.a.v, 16, m.a.s);
+                m.redge_off--;
+                m.rem--;
+            } while (m.rem);
+            m.a.vr += m.a.v;
+            snprintd(m.a.vr, 16, m.a.sr);
+        }
+
+        m.prev_op_off = m.op_off;
+    } while (m.prev_op_off != fop_off);
+
+    return m.a.vr;
+}
+
+#define RUN_TEST1 1
+#define RUN_PART1 1
+#define RUN_TEST2 1
+#define RUN_PART2 1
+
+#define TEST1_EXPECT 4277556
+#define TEST2_EXPECT 3263827
+
+void run() {
+#if RUN_TEST1
+    print("PART 1 TEST: ");
+    if (num v = do_part1(countof(test), test); v != TEST1_EXPECT) {
+        print("FAILED (got ");
+        printd(v);
+        print(", expected " xstr(TEST1_EXPECT) ")\n");
+    } else {
+        print("PASSED\n");
+    }
+#endif
+
+#if RUN_PART1
+    print("PART 1 RESULT: ");
+    printd(do_part1(countof(input), input));
+    print("\n");
+#endif
+
+#if RUN_TEST2
+    print("PART 2 TEST: ");
+    if (num v = do_part2(countof(test), test); v != TEST2_EXPECT) {
+        print("FAILED (got ");
+        printd(v);
+        print(", expected " xstr(TEST2_EXPECT) ")\n");
+    } else {
+        print("PASSED\n");
+    }
+#endif
+
+#if RUN_PART2
+    print("PART 2 RESULT: ");
+    printd(do_part2(countof(input), input));
+    print("\n");
+#endif
+
+    exit_group(0);
+}

day7.c

@@ -0,0 +1,178 @@
+#include "lib.h"
+
+#define DBG 0
+
+static
+ch input[32768] = {
+#embed "day7_input.txt"
+};
+
+static
+ch test[512] = {
+#embed "day7_test.txt"
+};
+
+typedef struct { ch l[64]; } line;
+static_assert(sizeof(line) == 0x40);
+
+alignas(0x40) static
+struct {
+    line padstart[4];
+    num file_stride;
+    num stride;
+    num _extra[6];
+    union { line l; struct { ch s[16]; num n; }; } result;
+    line padend;
+} m;
+static_assert(offsetof(typeof(m),result) % 64 == 0);
+static_assert(offsetof(typeof(m),padend) % 64 == 0);
+
+alignas(4096) ch buf1[256];
+alignas(4096) num buf[256];
+
+static
+num do_part1(size_t file_len, ch file[file_len]) {
+    m = (typeof(m)){ };
+    m.result.n = 0;
+#if DBG
+        pnl();
+#endif
+
+    memset(buf1, 0, sizeof(buf1));
+
+    m.file_stride = findc(file, '\n', file_len) - file;
+    num linecnt = (findc(file, 0, file_len) - file) / m.file_stride;
+#if DBG
+    print("stride "); printd(m.file_stride); pnl();
+    print("lines  "); printd(linecnt); pnl();
+#endif
+
+    num s_pos = findc(file, 'S', - 1) - 1 - file;
+    buf1[s_pos] = '|';
+    num line = 2;
+    do {
+        ch *l = file + line * m.file_stride;
+        for (num col = 0; col < m.file_stride - 1; col++) {
+            ch c = l[col];
+            if (c == '^') {
+                m.result.n += buf1[col] > 0;
+                buf1[col-1] |= buf1[col];
+                buf1[col+1] |= buf1[col];
+                buf1[col] = 0;
+            }
+        }
+#if DBG
+        for (num col = 0; col < m.file_stride; col++) {
+            if (buf1[col] == '|') print("|");
+            else if (l[col] == '^') print("^");
+            else print(" ");
+        }
+        pnl();
+#endif
+        line+=2;
+    } while (line < linecnt);
+
+    return m.result.n;
+}
+
+static
+num do_part2(size_t file_len, ch file[file_len]) {
+    m = (typeof(m)){ };
+#if DBG
+        pnl();
+#endif
+
+    memset(buf, 0, sizeof(buf));
+
+    m.file_stride = findc(file, '\n', file_len) - file;
+    num linecnt = (findc(file, 0, file_len) - file) / m.file_stride;
+#if DBG
+    print("stride "); printd(m.file_stride); pnl();
+    print("lines  "); printd(linecnt); pnl();
+#endif
+
+    num s_pos = findc(file, 'S', - 1) - 1 - file;
+    buf[s_pos] = 1;
+    num line = 2;
+    do {
+        ch *l = file + line * m.file_stride;
+        for (num col = 0; col < m.file_stride - 1; col++) {
+            ch c = l[col];
+            if (c == '^') {
+                buf[col-1] += buf[col];
+                buf[col+1] += buf[col];
+                buf[col] = 0;
+            }
+        }
+        for (num col = 0; col < m.file_stride; col++) {
+            num v = buf[col];
+#if DBG
+            if (l[col] == '^') print(" ");
+            else if (v >> 32) print("█");
+            else if (v >> 16) print("▓");
+            else if (v >>  8) print("▒");
+            else if (v >>  4) print("░");
+            else if (v >>  2) print("-");
+            else if (v >>  0) print(".");
+            else print(" ");
+#endif
+        }
+#if DBG
+        pnl();
+#endif
+        line+=2;
+    } while (line < linecnt);
+
+    m.result.n = 0;
+    for (num col = 0; col < m.file_stride; col++) {
+        m.result.n += buf[col];
+    }
+
+    return m.result.n;
+}
+
+#define RUN_TEST1 1
+#define RUN_PART1 1
+#define RUN_TEST2 1
+#define RUN_PART2 1
+
+#define TEST1_EXPECT 21
+#define TEST2_EXPECT 40
+
+void run() {
+#if RUN_TEST1
+    print("PART 1 TEST: ");
+    if (num v = do_part1(countof(test), test); v != TEST1_EXPECT) {
+        print("FAILED (got ");
+        printd(v);
+        print(", expected " xstr(TEST1_EXPECT) ")\n");
+    } else {
+        print("PASSED\n");
+    }
+#endif
+
+#if RUN_PART1
+    print("PART 1 RESULT: ");
+    printd(do_part1(countof(input), input));
+    print("\n");
+#endif
+
+#if RUN_TEST2
+    print("PART 2 TEST: ");
+    if (num v = do_part2(countof(test), test); v != TEST2_EXPECT) {
+        print("FAILED (got ");
+        printd(v);
+        print(", expected " xstr(TEST2_EXPECT) ")\n");
+    } else {
+        print("PASSED\n");
+    }
+#endif
+
+#if RUN_PART2
+    print("PART 2 RESULT: ");
+    printd(do_part2(countof(input), input));
+    print("\n");
+#endif
+
+    exit_group(0);
+}

day8.c

@@ -0,0 +1,317 @@
+#include "lib.h"
+#include <stdlib.h>
+
+#define DBG 0
+
+static
+ch input[] = {
+#embed "day8_input.txt"
+};
+
+static
+ch test[] = {
+#embed "day8_test.txt"
+};
+
+
+typedef num point __attribute__((vector_size(4*sizeof(num))));
+
+alignas(64) static
+point positions[1000];
+
+alignas(64) static
+unsigned short circuits[1000];
+
+alignas(1024) static
+struct { num min_dist; unsigned short min_target; } targets[1000][1024];
+
+alignas(64) static
+unsigned short next_targets[1000];
+
+alignas(64) static
+num next_dists[1000];
+
+alignas(64) static
+unsigned short next_indices[1000];
+
+static
+int targetcompar(const void *a, const void *b) {
+    const num ad = ((typeof(**targets)*)a)->min_dist;
+    const num bd = ((typeof(**targets)*)b)->min_dist;
+    if (ad > bd) return 1;
+    else if (ad < bd) return -1;
+    else return 0;
+}
+
+static
+num do_part1(size_t file_len, ch file[file_len], bool istest) {
+    const num iters = istest ? 10 : 1000;
+    const num pointcount = istest ? 20 : 1000;
+    num iter = 0;
+#if DBG
+    pnl();
+#endif
+
+    // read in positions from file
+    { ch *s = file;
+    for (num i = 0; i < pointcount; i++) {
+        unsigned x = grabnum(s, &s);
+        s++;
+        unsigned y = grabnum(s, &s);
+        s++;
+        unsigned z = grabnum(s, &s);
+        s++;
+        positions[i] = (point){ x,y,z };
+    } }
+    // set up initial circuits
+    for (num i = 0; i < pointcount; i += 4) {
+        circuits[i+0] = i+0;
+        circuits[i+1] = i+1;
+        circuits[i+2] = i+2;
+        circuits[i+3] = i+3;
+    }
+    // find distances between all points
+    for (num i = 0; i < pointcount; i++) {
+        point pi = positions[i];
+        for (num j = 0; j < pointcount; j += 4) {
+            point pj0 = positions[j+0];
+            point pj1 = positions[j+1];
+            point pj2 = positions[j+2];
+            point pj3 = positions[j+3];
+
+            point dvp0 = (pi - pj0) * (pi - pj0);
+            point dvp1 = (pi - pj1) * (pi - pj1);
+            point dvp2 = (pi - pj2) * (pi - pj2);
+            point dvp3 = (pi - pj3) * (pi - pj3);
+
+            num d0 = dvp0[0] + dvp0[1] + dvp0[2] + dvp0[3];
+            num d1 = dvp1[0] + dvp1[1] + dvp1[2] + dvp1[3];
+            num d2 = dvp2[0] + dvp2[1] + dvp2[2] + dvp2[3];
+            num d3 = dvp3[0] + dvp3[1] + dvp3[2] + dvp3[3];
+
+            targets[i][j+0] = (typeof(**targets)) { d0, j+0 };
+            targets[i][j+1] = (typeof(**targets)) { d1, j+1 };
+            targets[i][j+2] = (typeof(**targets)) { d2, j+2 };
+            targets[i][j+3] = (typeof(**targets)) { d3, j+3 };
+        }
+        // sort targets. slow.
+        qsort(targets[i], pointcount, sizeof(**targets), targetcompar);
+    }
+    // set up initial next targets
+    for (num i = 0; i < pointcount; i++) {
+        next_targets[i] = targets[i][1].min_target;
+        next_dists[i]   = targets[i][1].min_dist;
+        next_indices[i] = 1;
+    }
+
+    // FIXED JOIN ITERATIONS
+    do {
+        // find min dist
+        num min_dist = -1;
+        num min_i = 0;
+        for (num i = 0; i < pointcount; i++)
+            if (next_dists[i] < min_dist)
+                min_dist = next_dists[min_i = i];
+        num min_j = next_targets[min_i];
+        // -- join the pair --
+#if DBG
+        point ipos = positions[min_i];
+        point jpos = positions[min_j];
+        printd(ipos[0]); print(","); printd(ipos[1]); print(","); printd(ipos[2]);
+        print("\t->\t");
+        printd(jpos[0]); print(","); printd(jpos[1]); print(","); printd(jpos[2]);
+        pnl();
+#endif
+        // update circuits
+        unsigned old_circuit = circuits[min_j];
+        unsigned new_circuit = circuits[min_i];
+        if (old_circuit != new_circuit) {
+            for (num c = 0; c < pointcount; c++)
+                if (circuits[c] == old_circuit)
+                    circuits[c] = new_circuit;
+        }
+        // update targets
+        unsigned niidx = ++next_indices[min_i];
+        unsigned njidx = ++next_indices[min_j];
+        next_targets[min_i] = targets[min_i][niidx].min_target;
+        next_targets[min_j] = targets[min_j][njidx].min_target;
+        next_dists[min_i] = targets[min_i][niidx].min_dist;
+        next_dists[min_j] = targets[min_j][njidx].min_dist;
+
+        iter++;
+    } while(iter < iters);
+
+    // reuse next_targets to store circuit counts
+    for (num i = 0; i < pointcount; i++) {
+        next_targets[i] = 0;
+    }
+    for (num i = 0; i < pointcount; i++) {
+        next_targets[circuits[i]]++;
+    }
+    num circ0 = 0, circ1 = 0, circ2 = 0;
+    for (num i = 0; i < pointcount; i++) {
+        if (next_targets[i] > circ0) {
+            circ2 = circ1;
+            circ1 = circ0;
+            circ0 = next_targets[i];
+        } else if (next_targets[i] > circ1) {
+            circ2 = circ1;
+            circ1 = next_targets[i];
+        } else if (next_targets[i] > circ2) {
+            circ2 = next_targets[i];
+        }
+    }
+
+    return circ0 * circ1 * circ2;
+}
+
+static
+num do_part2(size_t file_len, ch file[file_len], bool istest) {
+    const num pointcount = istest ? 20 : 1000;
+#if DBG
+    pnl();
+#endif
+
+    // read in positions from file
+    { ch *s = file;
+    for (num i = 0; i < pointcount; i++) {
+        unsigned x = grabnum(s, &s);
+        s++;
+        unsigned y = grabnum(s, &s);
+        s++;
+        unsigned z = grabnum(s, &s);
+        s++;
+        positions[i] = (point){ x,y,z };
+    } }
+    // set up initial circuits
+    for (num i = 0; i < pointcount; i += 4) {
+        circuits[i+0] = i+0;
+        circuits[i+1] = i+1;
+        circuits[i+2] = i+2;
+        circuits[i+3] = i+3;
+    }
+    // find distances between all points
+    for (num i = 0; i < pointcount; i++) {
+        point pi = positions[i];
+        for (num j = 0; j < pointcount; j += 4) {
+            point pj0 = positions[j+0];
+            point pj1 = positions[j+1];
+            point pj2 = positions[j+2];
+            point pj3 = positions[j+3];
+
+            point dvp0 = (pi - pj0) * (pi - pj0);
+            point dvp1 = (pi - pj1) * (pi - pj1);
+            point dvp2 = (pi - pj2) * (pi - pj2);
+            point dvp3 = (pi - pj3) * (pi - pj3);
+
+            num d0 = dvp0[0] + dvp0[1] + dvp0[2] + dvp0[3];
+            num d1 = dvp1[0] + dvp1[1] + dvp1[2] + dvp1[3];
+            num d2 = dvp2[0] + dvp2[1] + dvp2[2] + dvp2[3];
+            num d3 = dvp3[0] + dvp3[1] + dvp3[2] + dvp3[3];
+
+            targets[i][j+0] = (typeof(**targets)) { d0, j+0 };
+            targets[i][j+1] = (typeof(**targets)) { d1, j+1 };
+            targets[i][j+2] = (typeof(**targets)) { d2, j+2 };
+            targets[i][j+3] = (typeof(**targets)) { d3, j+3 };
+        }
+        // sort targets. slow.
+        qsort(targets[i], pointcount, sizeof(**targets), targetcompar);
+    }
+    // set up initial next targets
+    for (num i = 0; i < pointcount; i++) {
+        next_targets[i] = targets[i][1].min_target;
+        next_dists[i]   = targets[i][1].min_dist;
+        next_indices[i] = 1;
+    }
+
+    unsigned last_i = 0, last_j = 0;
+    // main iterations
+    do {
+        // find min dist
+        num min_dist = -1;
+        num min_i = 0;
+        for (num i = 0; i < pointcount; i++)
+            if (next_dists[i] < min_dist)
+                min_dist = next_dists[min_i = i];
+        num min_j = next_targets[min_i];
+        last_i = min_i;
+        last_j = min_j;
+        // -- join the pair --
+#if DBG
+        point ipos = positions[min_i];
+        point jpos = positions[min_j];
+        printd(ipos[0]); print(","); printd(ipos[1]); print(","); printd(ipos[2]);
+        print("\t->\t");
+        printd(jpos[0]); print(","); printd(jpos[1]); print(","); printd(jpos[2]);
+        pnl();
+#endif
+        // update circuits
+        unsigned old_circuit = circuits[min_j];
+        unsigned new_circuit = circuits[min_i];
+        if (old_circuit != new_circuit) {
+            bool done = true;
+            for (num c = 0; c < pointcount; c++) {
+                if (circuits[c] == old_circuit)
+                    circuits[c] = new_circuit;
+                if (circuits[c] != new_circuit)
+                    done = false;
+            }
+            if (done) break;
+        }
+        // update targets
+        unsigned niidx = ++next_indices[min_i];
+        unsigned njidx = ++next_indices[min_j];
+        next_targets[min_i] = targets[min_i][niidx].min_target;
+        next_targets[min_j] = targets[min_j][njidx].min_target;
+        next_dists[min_i] = targets[min_i][niidx].min_dist;
+        next_dists[min_j] = targets[min_j][njidx].min_dist;
+    } while(true);
+
+    return positions[last_i][0] * positions[last_j][0];
+}
+
+#define RUN_TEST1 1
+#define RUN_PART1 1
+#define RUN_TEST2 1
+#define RUN_PART2 1
+
+#define TEST1_EXPECT 40
+#define TEST2_EXPECT 25272
+
+void run() {
+#if RUN_TEST1
+    print("PART 1 TEST: ");
+    if (num v = do_part1(countof(test), test, true); v != TEST1_EXPECT) {
+        print("FAILED (got ");
+        printd(v);
+        print(", expected " xstr(TEST1_EXPECT) ")\n");
+    } else {
+        print("PASSED\n");
+    }
+#endif
+
+#if RUN_PART1
+    print("PART 1 RESULT: ");
+    printd(do_part1(countof(input), input, false));
+    print("\n");
+#endif
+
+#if RUN_TEST2
+    print("PART 2 TEST: ");
+    if (num v = do_part2(countof(test), test, true); v != TEST2_EXPECT) {
+        print("FAILED (got ");
+        printd(v);
+        print(", expected " xstr(TEST2_EXPECT) ")\n");
+    } else {
+        print("PASSED\n");
+    }
+#endif
+
+#if RUN_PART2
+    print("PART 2 RESULT: ");
+    printd(do_part2(countof(input), input, false));
+    print("\n");
+#endif
+
+    exit_group(0);
+}

lib.h

@@ -35,6 +35,37 @@ void exit_group(uint64_t code) {
 
 typedef uint64_t bcdint;
 typedef uint64_t num;
+typedef unsigned char ch;
+
+__attribute__((always_inline)) inline
+ch *findc(const ch *s, ch c, size_t n) {
+    uint64_t dispose;
+    void *d;
+    asm("repnz scasb":"=D"(d),"=c"(dispose):"D"(s),"c"(n),"a"(c):"memory","cc");
+    return d;
+}
+
+__attribute__((always_inline)) inline
+num *findnum(const num *s, num c, size_t n) {
+    uint64_t dispose;
+    void *d;
+    asm("repnz scasq":"=D"(d),"=c"(dispose):"D"(s),"c"(n),"a"(c):"memory","cc");
+    return d;
+}
+
+__attribute__((always_inline)) inline
+num *findnotnum(const num *s, num c, size_t n) {
+    uint64_t dispose;
+    void *d;
+    asm("repz scasq":"=D"(d),"=c"(dispose):"D"(s),"c"(n),"a"(c):"memory","cc");
+    return d;
+}
+
+static inline num alignnum(num v, num align) {
+    num extra = v % align;
+    num adjust = (align - extra) % align;
+    return v + adjust;
+}
 
 static
 void printns(size_t len, unsigned char chars[len]) {
@@ -63,6 +94,7 @@ void print_many_char(size_t len, char chars[len]) {
 }
 
 #define print(string) print_many_char(sizeof(string)-1, string)
+#define pnl() print("\n")
 
 static
 void printd(unsigned long v) {