add SHA256 benchmark via the Unix tool and pipes

hash/cpu/bench/SHA256/Unix/build.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+gcc -O3 fakedata.c

hash/cpu/bench/SHA256/Unix/fakedata.c

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+
+// generate given amount of fake data to be hashed, and push it to standard output
+
+#include <stdio.h>
+#include <stdlib.h>
+
+void generate(megabytes) {
+  
+  unsigned char buffer[257];
+  for(int i=0;i<256;i++) { buffer[i] = 1+(i%255); }
+  buffer[256] = 0;
+
+  for(int i=0;i<megabytes;i++) {
+    for(int j=0;j<4096;j++) {
+      fputs( (char*)buffer, stdout);
+    }
+  }
+
+}
+
+int main( int argc, char *argv[] ) {
+  
+  int megabytes = 1;
+  switch(argc) {
+
+    case 2:
+      megabytes = atoi(argv[1]);
+      generate(megabytes);
+      break;
+
+    default:
+      printf("usage:\n");
+      printf("$ fakedata <amount_in_megabytes>:\n");
+      exit(-1);
+      break;
+
+  }
+}

hash/cpu/bench/SHA256/Unix/run.sh

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+#!/bin/bash
+
+./a.out $ZKBENCH_MEGABYTES | shasum -a256 -b -