From 74a9bee9e67e9800d8efe164d66f5c479f7fabca Mon Sep 17 00:00:00 2001
From: Bond_009 <bond.009@outlook.com>
Date: Thu, 3 Dec 2020 21:37:22 +0100
Subject: Add fast AVX version of day 1 part 2

---
 1/part2_fast.c | 138 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 138 insertions(+)
 create mode 100644 1/part2_fast.c

diff --git a/1/part2_fast.c b/1/part2_fast.c
new file mode 100644
index 0000000..1d9afb1
--- /dev/null
+++ b/1/part2_fast.c
@@ -0,0 +1,138 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <immintrin.h>
+
+#define INPUT_LEN 200
+#define SEARCH 2020
+
+int inner_repair_avx(int i, const int *arr, __m256i search)
+{
+    __m256i start = _mm256_set1_epi32(i);
+    for (int k = 0; k < INPUT_LEN; k += 8) {
+        __m256i new = _mm256_loadu_si256((__m256i *)(&arr[k]));
+        new = _mm256_add_epi32(start, new);
+        int mask = _mm256_movemask_epi8(_mm256_cmpeq_epi32(new, search));
+        if (mask == 0) {
+            continue;
+        }
+
+        for (int l = 0; l < 8; l++) {
+            if (mask & (0xf << (l * 4))) {
+                return arr[k + l];
+            }
+        }
+    }
+
+    return 0;
+}
+
+int repair_avx(const int *arr)
+{
+    __m256i search = _mm256_set1_epi32(SEARCH);
+    for (int i = 0; i < INPUT_LEN; i++) {
+        __m256i start = _mm256_set1_epi32(arr[i]);
+        for (int j = 0; j < INPUT_LEN; j += 8) {
+            __m256i new = _mm256_loadu_si256((__m256i *)(&arr[j]));
+            new = _mm256_add_epi32(start, new);
+            int mask = _mm256_movemask_epi8(_mm256_cmpgt_epi32(new, search));
+            if (mask == 0xffffffff) {
+                continue;
+            }
+
+            switch (__lzcnt32(mask) / 4) {
+                case 0: goto label0;
+                case 1: goto label1;
+                case 2: goto label2;
+                case 3: goto label3;
+                case 4: goto label4;
+                case 5: goto label5;
+                case 6: goto label6;
+                case 7: goto label7;
+            }
+
+        label0:
+            if ((mask & 0x0000000f) == 0) {
+                int tmp = inner_repair_avx(_mm256_extract_epi32(new, 0), arr, search);
+                if (tmp) {
+                    return tmp * arr[i] * arr[j];
+                }
+            }
+
+        label1:
+            if ((mask & 0x000000f0) == 0) {
+                int tmp = inner_repair_avx(_mm256_extract_epi32(new, 1), arr, search);
+                if (tmp) {
+                    return tmp * arr[i] * arr[j + 1];
+                }
+            }
+
+        label2:
+            if ((mask & 0x00000f00) == 0) {
+                int tmp = inner_repair_avx(_mm256_extract_epi32(new, 2), arr, search);
+                if (tmp) {
+                    return tmp * arr[i] * arr[j + 2];
+                }
+            }
+
+        label3:
+            if ((mask & 0x0000f000) == 0) {
+                int tmp = inner_repair_avx(_mm256_extract_epi32(new, 3), arr, search);
+                if (tmp) {
+                    return tmp * arr[i] * arr[j + 3];
+                }
+            }
+
+        label4:
+            if ((mask & 0x000f0000) == 0) {
+                int tmp = inner_repair_avx(_mm256_extract_epi32(new, 4), arr, search);
+                if (tmp) {
+                    return tmp * arr[i] * arr[j + 4];
+                }
+            }
+
+        label5:
+            if ((mask & 0x00f00000) == 0 ){
+                int tmp = inner_repair_avx(_mm256_extract_epi32(new, 5), arr, search);
+                if (tmp) {
+                    return tmp * arr[i] * arr[j + 5];
+                }
+            }
+
+        label6:
+            if ((mask & 0x0f000000) == 0) {
+                int tmp = inner_repair_avx(_mm256_extract_epi32(new, 6), arr, search);
+                if (tmp) {
+                    return tmp * arr[i] * arr[j + 6];
+                }
+            }
+
+        label7:
+            if ((mask & 0xf0000000) == 0) {
+                int tmp = inner_repair_avx(_mm256_extract_epi32(new, 7), arr, search);
+                if (tmp) {
+                    return tmp * arr[i] * arr[j + 7];
+                }
+            }
+        }
+    }
+
+    return 0;
+}
+
+int main()
+{
+    FILE *file = fopen("input", "r");
+
+    char buffer[8] = { 0 };
+    int input[INPUT_LEN] = { 0 };
+    for (int i = 0; i < 200; i++) {
+        fgets(buffer, 8, file);
+        input[i] = atoi(buffer);
+    }
+
+    fclose(file);
+
+    printf("%i\n", repair_avx(input));
+}
-- 
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