From 4e09bca9e34c226b6d7e34b4fa11248405fd988e Mon Sep 17 00:00:00 2001
From: Anton Kling <anton@kling.gg>
Date: Sun, 22 Oct 2023 19:50:38 +0200
Subject: Move everything into a new repo.

---
 userland/libc/stdlib/strtod.c | 70 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 userland/libc/stdlib/strtod.c

(limited to 'userland/libc/stdlib/strtod.c')

diff --git a/userland/libc/stdlib/strtod.c b/userland/libc/stdlib/strtod.c
new file mode 100644
index 0000000..2c83879
--- /dev/null
+++ b/userland/libc/stdlib/strtod.c
@@ -0,0 +1,70 @@
+#include <ctype.h>
+#include <stdlib.h>
+#include <assert.h>
+
+int ctoi(char c) { return c - '0'; }
+
+double strtod(const char *restrict nptr, char **restrict endptr) {
+  double r = 0;
+  // An initial, possibly empty, sequence of white-space characters (as
+  // specified by isspace())
+  for (; isspace(*nptr); nptr++)
+    ;
+
+  // A subject sequence interpreted as a floating-point constant or representing
+  // infinity or NaN
+
+  {
+    // The expected form of the subject sequence is an optional '+' or '-' sign
+    int sign = 0;
+    int exp_sign = 0;
+    if ('+' == *nptr) {
+      sign = 0;
+      nptr++;
+    } else if ('-' == *nptr) {
+      sign = 1;
+      nptr++;
+    }
+
+    // A non-empty sequence of decimal digits optionally containing a radix
+    // character
+    double exp = 0;
+    for (; isdigit(*nptr); nptr++) {
+      r *= 10;
+      r += ctoi(*nptr);
+    }
+    if ('.' == *nptr) {
+      double div = 10;
+      for (; isdigit(*nptr); nptr++) {
+        r += ctoi(*nptr) / div;
+        div *= 10;
+      }
+    }
+    r *= (sign) ? (-1) : (1);
+
+    // then an optional exponent part consisting of the character 'e' or
+    // the character 'E'
+    if ('e' == tolower(*nptr)) {
+      // optionally followed by a '+' or '-' character
+      if ('+' == *nptr) {
+        exp_sign = 0;
+        nptr++;
+      } else if ('-' == *nptr) {
+        exp_sign = 1;
+        nptr++;
+      }
+      // and then followed by one or more decimal digits
+      for (; isdigit(*nptr); nptr++) {
+        exp *= 10;
+        exp += ctoi(*nptr);
+      }
+      exp *= (exp_sign) ? (-1) : (1);
+    }
+    assert(0 == exp); // TODO
+  }
+
+  // A final string of one or more unrecognized characters, including the
+  // terminating NUL character of the input string
+  ;
+  return r;
+}
-- 
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