From 94147b887b26453576d722e2b96d33571809e67d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=B6rg=20Sommer?= <joerg@alea.gnuu.de>
Date: Wed, 29 Mar 2017 13:15:45 +0200
Subject: [PATCH] =?UTF-8?q?J=C3=B6rgs=20L=C3=B6sung=20f=C3=BCr=20Euler=208?=
 =?UTF-8?q?7=20in=20C?=
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---
 2017-03-28/Makefile        |  11 ++++
 2017-03-28/jo-so_euler87.c | 108 +++++++++++++++++++++++++++++++++++++
 2 files changed, 119 insertions(+)
 create mode 100644 2017-03-28/Makefile
 create mode 100644 2017-03-28/jo-so_euler87.c

diff --git a/2017-03-28/Makefile b/2017-03-28/Makefile
new file mode 100644
index 0000000..26afcda
--- /dev/null
+++ b/2017-03-28/Makefile
@@ -0,0 +1,11 @@
+#!/usr/bin/make -f
+
+CFLAGS=-g -O2 -fPIC -fPIE -Wall -Wextra -Wformat=2 -Wunused -Wlogical-op -Wundef \
+	-Wswitch-enum -Wpointer-arith -Wcast-qual -Wcast-align -Wwrite-strings \
+	-Wconversion -D_FORTIFY_SOURCE=2 -fstack-protector -Wshadow -Wnested-externs
+
+LDFLAGS=-lm
+
+.PHONY: all
+
+all: jo-so_euler87
diff --git a/2017-03-28/jo-so_euler87.c b/2017-03-28/jo-so_euler87.c
new file mode 100644
index 0000000..b0245ec
--- /dev/null
+++ b/2017-03-28/jo-so_euler87.c
@@ -0,0 +1,108 @@
+#include <math.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+static int cmp_uint(const void* p1, const void* p2)
+{
+    const uint a = *(const uint*)p1;
+    const uint b = *(const uint*)p2;
+    if (a < b)
+        return -1;
+    if (a == b)
+        return 0;
+    return 1;
+}
+
+int main(void)
+{
+    const uint LIMIT = 50000000;
+    uint* const prime_numbers = malloc(4096);
+    if (prime_numbers == NULL)
+    {
+        perror("Failed to allocate memory for prime numbers");
+        return EXIT_FAILURE;
+    }
+    uint* const prime_numbers_end = prime_numbers + 4096 / sizeof(*prime_numbers);
+
+    uint max_pn = (uint)sqrt(LIMIT);
+    prime_numbers[0] = 2u;
+    prime_numbers[1] = 3u;
+    uint* next_pn = &prime_numbers[2];
+
+    for (uint num = *(next_pn - 1) + 2; num <= max_pn; num += 2)
+    {
+        for (uint i = (uint)sqrt(num); i >= 3; --i)
+        {
+            if (num % i == 0)
+                goto next;
+        }
+        if (next_pn >= prime_numbers_end)
+        {
+            fprintf(stderr, "Memory for prime numbers exceeded, but more needed.\n");
+            return EXIT_FAILURE;
+        }
+
+        *next_pn++ = num;
+    next:
+        ;
+    }
+
+    printf("There are %ld numbers below sqrt(50.000.000)\n", next_pn - prime_numbers);
+
+    uint* nums = NULL;
+    uint* nums_end = nums;
+    uint* next_num = nums;
+
+    for (uint* pn2 = prime_numbers; pn2 < next_pn; ++pn2)
+    {
+        uint pow2 = *pn2 * *pn2;
+
+        for (uint* pn3 = prime_numbers; pn3 < next_pn; ++pn3)
+        {
+            uint pow3 = *pn3 * *pn3 * *pn3;
+
+            uint sum = pow2 + pow3;
+            if (sum >= LIMIT)
+                break;
+
+            for (uint* pn4 = prime_numbers; pn4 < next_pn; ++pn4)
+            {
+                uint pow4 = *pn4 * *pn4;
+                pow4 *= pow4;
+
+                uint sum2 = sum + pow4;
+                if (sum2 >= LIMIT)
+                    break;
+
+                if (next_num >= nums_end)
+                {
+                    long next_num_idx = next_num - nums;
+                    size_t new_size = (uint)(nums_end - nums) * sizeof(*nums) + (1 << 20);
+                    nums = realloc(nums, new_size);
+                    if (nums == NULL)
+                    {
+                        perror("Failed to increase memory for result numbers");
+                        return EXIT_FAILURE;
+                    }
+
+                    nums_end = nums + new_size / sizeof(*nums);
+                    next_num = &nums[next_num_idx];
+                }
+
+                *next_num++ = sum2;
+            }
+        }
+    }
+    nums_end = next_num;
+
+    qsort(nums, (size_t)(nums_end - nums), sizeof(*nums), cmp_uint);
+
+    uint count = 1;
+    for (const uint* n = nums + 1; n < nums_end; ++n)
+        if (*(n - 1) != *n)
+            ++count;
+
+    printf("Answer: %d\n", count);
+
+    return EXIT_SUCCESS;
+}