From d9c9d465dffb2ed67e43cf9425f30dae6012e93a Mon Sep 17 00:00:00 2001
From: Andrew Bettison <andrew@servalproject.org>
Date: Tue, 20 Sep 2016 15:46:17 +0930
Subject: [PATCH] Add approximate scaled format functions

Used to produce human-readable values in logs, reports etc.
Eg: 1,073,741,824 -> "1.07g" (SI) and "1.00G" (binary).
---
 numeric_str.c | 29 +++++++++++++++++++++++++++++
 numeric_str.h | 20 ++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/numeric_str.c b/numeric_str.c
index c826bb02..2ac411ed 100644
--- a/numeric_str.c
+++ b/numeric_str.c
@@ -304,3 +304,32 @@ int str_to_uint64_interval_ms(const char *str, int64_t *result, const char **aft
   return 1;
 }
 
+strbuf strbuf_append_double_scaled_binary(strbuf sb, double value)
+{
+  const char *suffix = " KMGTP";
+  while (value >= 1024 && suffix[1]){
+    value = value / 1024;
+    suffix++;
+  }
+  int precision = value < 10 ? 2 : value < 100 ? 1 : 0;
+  strbuf_sprintf(sb, "%.*f", precision, value);
+  if (*suffix && *suffix != ' ') {
+    strbuf_putc(sb, *suffix);
+  }
+  return sb;
+}
+
+strbuf strbuf_append_double_scaled_si(strbuf sb, double value)
+{
+  const char *suffix = " kmgtp";
+  while (value >= 1000 && suffix[1]){
+    value = value / 1000;
+    suffix++;
+  }
+  int precision = value < 10 ? 2 : value < 100 ? 1 : 0;
+  strbuf_sprintf(sb, "%.*f", precision, value);
+  if (*suffix && *suffix != ' ') {
+    strbuf_putc(sb, *suffix);
+  }
+  return sb;
+}
diff --git a/numeric_str.h b/numeric_str.h
index 7f7cb453..4f426498 100644
--- a/numeric_str.h
+++ b/numeric_str.h
@@ -107,6 +107,26 @@ uint64_t scale_factor(const char *str, const char **afterp);
 strbuf strbuf_append_uint32_scaled(strbuf sb, uint32_t value);
 strbuf strbuf_append_uint64_scaled(strbuf sb, uint64_t value);
 
+/* Append a double value to a strbuf in ASCII decimal fixed-point format with three significant
+ * digits, optionally scaled with either a binary scale suffix in the set {KMGTP}: 'K' = 1<<10, 'M'
+ * = 1<<20, 'G' = * 1<<30, etc., or an S.I.  scale suffix in the set {kmgtp}: 'k' = 1e3, 'm' = 1e6,
+ * etc.  This format is lossy because it always applies the scale, which may truncate insignificant
+ * digits.
+ *
+ * Eg, binary               S.I.
+ *     1000 -> "1000"       1000 -> "1.00k"
+ *     1001 -> "1001"       1001 -> "1.00k"
+ *     1024 -> "1.00K"      1024 -> "1.02k"
+ *     1025 -> "1.00K"      1025 -> "1.03k"
+ *
+ * @author Andrew Bettison <andrew@servalproject.com>
+ */
+strbuf strbuf_append_double_scaled_binary(strbuf sb, double value);
+strbuf strbuf_append_double_scaled_si(strbuf sb, double value);
+
+#define alloca_double_scaled_binary(v) strbuf_str(strbuf_append_double_scaled_binary(strbuf_alloca(10), (v)))
+#define alloca_double_scaled_si(v)     strbuf_str(strbuf_append_double_scaled_si(strbuf_alloca(10), (v)))
+
 /* Parse a string as a time interval (seconds) in millisecond resolution.  Return the number of
  * milliseconds.  Valid strings are all unsigned ASCII decimal numbers with up to three digits after
  * the decimal point.