From: Jens Axboe <axboe@kernel.dk>
Date: Wed, 5 Oct 2011 06:43:47 +0000 (+0200)
Subject: Add IEEE 754 pack and unpack helpers
X-Git-Tag: fio-1.99~8
X-Git-Url: https://git.kernel.dk/?p=fio.git;a=commitdiff_plain;h=90f326d04602d0df35ca32f251dd6cc353d26a25;ds=sidebyside

Add IEEE 754 pack and unpack helpers

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/Makefile b/Makefile
index c89bb173..b361603b 100644
--- a/Makefile
+++ b/Makefile
@@ -14,7 +14,7 @@ SOURCE = gettime.c fio.c ioengines.c init.c stat.c log.c time.c filesetup.c \
 		rbtree.c smalloc.c filehash.c profile.c debug.c lib/rand.c \
 		lib/num2str.c $(wildcard crc/*.c) engines/cpu.c \
 		engines/mmap.c engines/sync.c engines/null.c engines/net.c \
-		memalign.c server.c client.c iolog.c
+		memalign.c server.c client.c iolog.c ieee754.c
 
 ifeq ($(UNAME), Linux)
   SOURCE += diskutil.c fifo.c blktrace.c helpers.c cgroup.c trim.c \
diff --git a/ieee754.c b/ieee754.c
new file mode 100644
index 00000000..0fbc7f0e
--- /dev/null
+++ b/ieee754.c
@@ -0,0 +1,83 @@
+/*
+ * Shamelessly lifted from Beej's Guide to Network Programming, found here:
+ *
+ * http://beej.us/guide/bgnet/output/html/singlepage/bgnet.html#serialization
+ *
+ * Below code was granted to the public domain.
+ */
+#include <inttypes.h>
+
+uint64_t pack754(long double f, unsigned bits, unsigned expbits)
+{
+	long double fnorm;
+	int shift;
+	long long sign, exp, significand;
+	unsigned significandbits = bits - expbits - 1; // -1 for sign bit
+
+	// get this special case out of the way
+	if (f == 0.0)
+		return 0;
+
+	// check sign and begin normalization
+	if (f < 0) {
+		sign = 1;
+		fnorm = -f;
+	} else {
+		sign = 0;
+		fnorm = f;
+	}
+
+	// get the normalized form of f and track the exponent
+	shift = 0;
+	while (fnorm >= 2.0) {
+		fnorm /= 2.0;
+		shift++;
+	}
+	while (fnorm < 1.0) {
+		fnorm *= 2.0;
+		shift--;
+	}
+	fnorm = fnorm - 1.0;
+
+	// calculate the binary form (non-float) of the significand data
+	significand = fnorm * ((1LL << significandbits) + 0.5f);
+
+	// get the biased exponent
+	exp = shift + ((1 << (expbits - 1)) - 1); // shift + bias
+
+	// return the final answer
+	return (sign << (bits - 1)) | (exp << (bits-expbits - 1)) | significand;
+}
+
+long double unpack754(uint64_t i, unsigned bits, unsigned expbits)
+{
+	long double result;
+	long long shift;
+	unsigned bias;
+	unsigned significandbits = bits - expbits - 1; // -1 for sign bit
+
+	if (i == 0)
+		return 0.0;
+
+	// pull the significand
+	result = (i & ((1LL << significandbits) - 1)); // mask
+	result /= (1LL << significandbits); // convert back to float
+	result += 1.0f; // add the one back on
+
+	// deal with the exponent
+	bias = (1 << (expbits - 1)) - 1;
+	shift = ((i >> significandbits) & ((1LL << expbits) - 1)) - bias;
+	while (shift > 0) {
+		result *= 2.0;
+		shift--;
+	}
+	while (shift < 0) {
+		result /= 2.0;
+		shift++;
+	}
+
+	// sign it
+	result *= (i >> (bits - 1)) & 1 ? -1.0 : 1.0;
+
+	return result;
+}
diff --git a/ieee754.h b/ieee754.h
new file mode 100644
index 00000000..2087da5e
--- /dev/null
+++ b/ieee754.h
@@ -0,0 +1,10 @@
+#ifndef FIO_IEEE754_H
+#define FIO_IEEE754_H
+
+extern uint64_t pack754(long double f, unsigned bits, unsigned expbits);
+extern long double unpack754(uint64_t i, unsigned bits, unsigned expbits);
+
+#define fio_double_to_uint64(val)	pack754((val), 64, 11)
+#define fio_uint64_to_double(val)	unpack754((val), 64, 11)
+
+#endif