Fold LIBC_RAND into LIBC_STDIO/TINYMATH/INTRIN

libc/stdio/rdrand.c

@@ -0,0 +1,81 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/intrin/asmflag.h"
+#include "libc/errno.h"
+#include "libc/nexgen32e/x86feature.h"
+#include "libc/stdio/rand.h"
+#include "libc/sysv/consts/grnd.h"
+
+STATIC_YOINK("rdrand_init");
+
+static dontinline uint64_t rdrand_failover(void) {
+  int f;
+  size_t i;
+  ssize_t r;
+  volatile uint64_t b;
+  register uint64_t x;
+  for (f = GRND_RANDOM | GRND_NONBLOCK, i = 0; i < 8; i += r) {
+    if ((r = getrandom((char *)&b + i, 8 - i, f)) <= 0) {
+      if (r == -1 && errno == EINTR) {
+        r = 0;
+      } else if (r == -1 && errno == EAGAIN) {
+        r = 0;
+        f = 0;
+      } else {
+        return rand64();
+      }
+    }
+  }
+  x = b;
+  b = 0;
+  return x;
+}
+
+/**
+ * Retrieves 64-bits of hardware random data from RDRAND instruction.
+ *
+ * If RDRAND isn't available (we check CPUID and we also disable it
+ * automatically for microarchitectures where it's slow or buggy) then
+ * we try getrandom(), RtlGenRandom(), or sysctl(KERN_ARND). If those
+ * aren't available then we try /dev/urandom and if that fails, we try
+ * getauxval(AT_RANDOM), and if not we finally use RDTSC and getpid().
+ *
+ * @note this function could block a nontrivial time on old computers
+ * @note this function is indeed intended for cryptography
+ * @note this function takes around 300 cycles
+ * @see rngset(), rdseed(), rand64()
+ * @asyncsignalsafe
+ * @vforksafe
+ */
+uint64_t rdrand(void) {
+  int i;
+  char cf;
+  uint64_t x;
+  if (X86_HAVE(RDRND)) {
+    for (i = 0; i < 10; ++i) {
+      asm volatile(CFLAG_ASM("rdrand\t%1")
+                   : CFLAG_CONSTRAINT(cf), "=r"(x)
+                   : /* no inputs */
+                   : "cc");
+      if (cf) return x;
+      asm volatile("pause");
+    }
+  }
+  return rdrand_failover();
+}