diff --git a/algorithm.md b/algorithm.md
index 2e646f3..e7b8773 100644
--- a/algorithm.md
+++ b/algorithm.md
@@ -19,25 +19,28 @@ This is done in two phases:
 
 imohash takes two parameters, as well as the message length:
 
-* sample size (s)
-* sampling threshold (t)
-* message length (L)
+- sample size (s)
+- sampling threshold (t)
+- message length (L)
 
-There are two mode of operation: **sampled** and **full**. Mode is
-determined as follows:
+There are two mode of operation: **sampled** and **full**.
+
+**Full** mode is a single hash of the entire message. While sampling is the key point of imohash, sometimes it doesn't make sense and a full hash is used. It is used when the message length is less than the sampling threshold, or is less than twice the sample size - 1 (in order to sample from the middle of the message). **Full** mode is also used when the sample size parameter is less than 1.
+
+In all other cases **sampled** mode is used. Summarized:
 
 ```
-if (s > 0) && (t > 0) && (L > t) && (t > 2s)
-  mode = sampled
-else
+if (s < 1) || (L < t) || (L < (2s - 1))
   mode = full
+else
+  mode = sampled
 ```
 
 ### Hash calculation
 
 The core hashing routine uses [MurmurHash3](https://code.google.com/p/smhasher/wiki/MurmurHash3) in a 128-bit configuration.
-Hashing in *Full* mode is identical to passing the entire
-message to Murmhash3.  *Sampled* mode constructs a new message using
+Hashing in **Full** mode is identical to passing the entire
+message to Murmhash3. **Sampled** mode constructs a new message using
 three samples from the original:
 
 Message M of length L is an array of bytes, M[0]...M[L-1]. If
@@ -51,6 +54,7 @@ S2 = M[L-s:L-1]
 
 h' = Murmur3(concat(S0, S1, S2))
 ```
+
 ### Size injection
 
 Size is inserted into the hash directly. This means that two files
@@ -119,8 +123,8 @@ threshold t.
 {16384, 131073, 131072, "808008282d3f3b53e1fd132cc51fcc1d"},
 {16384, 131072, 500000, "a0c21e44a0ba3bddee802a9d1c5332ca"},
 {50,    131072, 300000, "e0a712edd8815c606344aed13c44adcf"},
+{0,     100,    1000,  "e80753211a57ee0de67c756e98e00496"},
+{50,    9999,   1000,  "e80753211a57ee0de67c756e98e00496"},
+{501,   20,     1000,  "e80753211a57ee0de67c756e98e00496"},
+{501,   20,     1001,  "e9079899cffb46f60c8645a01f12f9c9"},
 ```
-
-
-
-
diff --git a/imohash.go b/imohash.go
index 655a755..5203c07 100644
--- a/imohash.go
+++ b/imohash.go
@@ -25,7 +25,6 @@ type ImoHash struct {
 	hasher          murmur3.Hash128
 	sampleSize      int
 	sampleThreshold int
-	bytesAdded      int
 }
 
 // New returns a new ImoHash using the default sample size
@@ -79,11 +78,10 @@ func (imo *ImoHash) Sum(data []byte) [Size]byte {
 // SumFile hashes a file using using the ImoHash parameters.
 func (imo *ImoHash) SumFile(filename string) ([Size]byte, error) {
 	f, err := os.Open(filename)
-	defer f.Close()
-
 	if err != nil {
 		return emptyArray, err
 	}
+	defer f.Close()
 
 	fi, err := f.Stat()
 	if err != nil {
@@ -104,27 +102,30 @@ func (imo *ImoHash) hashCore(f *io.SectionReader) ([Size]byte, error) {
 
 	imo.hasher.Reset()
 
-	if f.Size() < int64(imo.sampleThreshold) || imo.sampleSize < 1 {
+	msgLen := f.Size()
+	if imo.sampleSize < 1 ||
+		msgLen < int64(imo.sampleThreshold) ||
+		msgLen < int64(2*imo.sampleSize-1) {
 		if _, err := io.Copy(imo.hasher, f); err != nil {
 			return emptyArray, err
 		}
 	} else {
 		buffer := make([]byte, imo.sampleSize)
-		if _, err := f.Read(buffer); err != nil {
+		if _, err := io.ReadFull(f, buffer); err != nil {
 			return emptyArray, err
 		}
 		imo.hasher.Write(buffer) // these Writes never fail
 		if _, err := f.Seek(f.Size()/2, 0); err != nil {
 			return emptyArray, err
 		}
-		if _, err := f.Read(buffer); err != nil {
+		if _, err := io.ReadFull(f, buffer); err != nil {
 			return emptyArray, err
 		}
 		imo.hasher.Write(buffer)
 		if _, err := f.Seek(int64(-imo.sampleSize), 2); err != nil {
 			return emptyArray, err
 		}
-		if _, err := f.Read(buffer); err != nil {
+		if _, err := io.ReadFull(f, buffer); err != nil {
 			return emptyArray, err
 		}
 		imo.hasher.Write(buffer)
diff --git a/spec_test.go b/spec_test.go
index e46909d..4b903bb 100644
--- a/spec_test.go
+++ b/spec_test.go
@@ -25,12 +25,17 @@ func TestSpec(t *testing.T) {
 		{16384, 131073, 131072, "808008282d3f3b53e1fd132cc51fcc1d"},
 		{16384, 131072, 500000, "a0c21e44a0ba3bddee802a9d1c5332ca"},
 		{50, 131072, 300000, "e0a712edd8815c606344aed13c44adcf"},
+
+		{0, 100, 1000, "e80753211a57ee0de67c756e98e00496"},
+		{50, 9999, 1000, "e80753211a57ee0de67c756e98e00496"},
+		{501, 20, 1000, "e80753211a57ee0de67c756e98e00496"},
+		{501, 20, 1001, "e9079899cffb46f60c8645a01f12f9c9"},
 	}
 
 	for _, test := range tests {
 		i := NewCustom(test.s, test.t)
 		hashStr = fmt.Sprintf("%x", i.Sum(M(test.n)))
-		equal(t, hashStr, test.hash)
+		equal(t, test.hash, hashStr)
 	}
 }