From d2e4fcbbacb8c9da789b0dfc978a86f536071e56 Mon Sep 17 00:00:00 2001
From: Michael Davidsaver <mdavidsaver@gmail.com>
Date: Wed, 13 Jan 2016 20:58:58 -0500
Subject: [PATCH] compressRecord: LIFO doesn't zero pad

Change handling of OFF so that reading a partially
populated buffer doesn't pad with zero.

Simplify put_value() and get_array_info()
---
 src/std/rec/compressRecord.c | 103 ++++++++++++++---------------------
 1 file changed, 40 insertions(+), 63 deletions(-)

diff --git a/src/std/rec/compressRecord.c b/src/std/rec/compressRecord.c
index c0feaacfb..c86b31af5 100644
--- a/src/std/rec/compressRecord.c
+++ b/src/std/rec/compressRecord.c
@@ -108,67 +108,34 @@ static void monitor(compressRecord *prec)
     db_post_events(prec, prec->bptr, monitor_mask);
 }
 
-static void put_value_FIFO(compressRecord *prec, double *psource, int n)
-{
-    epicsInt32 offset = prec->off;
-    epicsInt32 nuse = prec->nuse;
-    epicsInt32 nsam = prec->nsam;
-    double *pdest = prec->bptr + offset;
-    int i;
-
-    for (i = 0; i < n; i++) {
-        *pdest = *psource++;
-        if (++offset >= nsam) {
-            pdest = prec->bptr;
-            offset = 0;
-        }
-        else
-            pdest++;
-    }
-    nuse += n;
-    if (nuse > nsam)
-        nuse = nsam;
-    prec->off = offset;
-    prec->nuse = nuse;
-    return;
-}
-
-static void put_value_LIFO(compressRecord *prec, double *psource, int n)
-{
-    epicsInt32 offset = prec->off;
-    epicsInt32 nuse = prec->nuse;
-    epicsInt32 nsam = prec->nsam; 
-    epicsInt32 start = offset - nuse;
-    double *pdest;
-    int i;
-    if(start<0) start += nsam;
-
-    for(i = 0; i < n; i++) {
-        if(--start < 0) start += nsam;
-        pdest = prec->bptr + start;
-        *pdest = *psource++;
-    }
-    nuse += n;
-    if(nuse > nsam) nuse = nsam;
-    offset = start + nuse;
-    if(offset>=nsam) offset -= nsam;
-
-    prec->off = offset;
-    prec->nuse = nuse;
-
-    return;
-}
-
 static void put_value(compressRecord *prec, double *psource, int n)
 {
-    switch(prec->balg) {
-       case bufferingALG_FIFO: put_value_FIFO(prec, psource, n); break;
-       case bufferingALG_LIFO: put_value_LIFO(prec, psource, n); break;
+    int fifo = prec->balg==bufferingALG_FIFO;
+    epicsUInt32 offset = prec->off;
+    epicsUInt32 nuse = prec->nuse;
+    epicsUInt32 nsam = prec->nsam;
+
+    nuse += n;
+    if(nuse>nsam)
+        nuse = nsam;
+
+    while(n--) {
+        /* for LIFO, decrement before */
+        if(!fifo)
+            offset = (offset-1)%nsam;
+
+        prec->bptr[offset] = *psource++;
+
+        /* for FIFO, increment after */
+        if(fifo)
+            offset = (offset+1)%nsam;
     }
-    return;
+
+    prec->off = offset;
+    prec->nuse = nuse;
 }
 
-
+
 /* qsort comparison function (for median calculation) */
 static int compare(const void *arg1, const void *arg2)
 {
@@ -434,13 +401,22 @@ static long cvt_dbaddr(DBADDR *paddr)
 
 static long get_array_info(DBADDR *paddr, long *no_elements, long *offset)
 {
+    /* offset indicates the next element which would be written.
+     * In FIFO mode offset-1 is the last valid element
+     * In LIFO mode offset is the first valid element
+     * (*offset) should be set to the index of the first valid element
+     */
     compressRecord *prec = (compressRecord *) paddr->precord;
-    epicsInt32 start = prec->off - prec->nuse;
-    if(start<0) start += prec->nsam;
-    if(prec->balg == bufferingALG_FIFO)
-         *no_elements = prec->nuse;
-    else *no_elements = prec->nsam;
-    *offset = start;
+    epicsUInt32 off = prec->off;
+    epicsUInt32 nuse = prec->nuse;
+    epicsUInt32 nsam = prec->nsam;
+
+    *no_elements = nuse;
+    if(prec->balg == bufferingALG_FIFO) {
+        *offset = (off-nuse)%nsam;
+    } else {
+        *offset = off;
+    }
 
     return 0;
 }
@@ -449,7 +425,8 @@ static long put_array_info(DBADDR *paddr, long nNew)
 {
     compressRecord *prec = (compressRecord *) paddr->precord;
 
-    prec->off = (prec->off + nNew) % prec->nsam;
+    if(prec->balg == bufferingALG_FIFO)
+        prec->off = (prec->off + nNew) % prec->nsam;
     prec->nuse += nNew;
     if (prec->nuse > prec->nsam)
         prec->nuse = prec->nsam;