fewer allocations

int2str.nim

@@ -56,8 +56,8 @@ proc countdigits(value:int32): int {.inline.} =
   result = (32 - countLeadingZeroBits(value or 1)) * 1233 shr 12
   result = result - int(value < powers_of_10[result]) + 1
 
-proc fastIntToStr*(value:int32, outstr:var string) {.inline.} =
-  outstr.setLen(countdigits(value))
+proc fastIntToStr*(value:int32, outstr:var string, offset:int=0) {.inline.} =
+  outstr.setLen(offset + countdigits(value))
   var value = value
   var L = outstr.high
   while value >= 100:
@@ -85,7 +85,7 @@ when isMainModule:
   var outstr = newString(10)
   for i in 0'i32..200_000_000:
     fastIntToStr(i, outstr)
-    #doAssert outstr == $i
+    doAssert outstr == $i
   echo cpuTime() - t0
 
   t0 = cpuTime()

mosdepth.nim

@@ -666,16 +666,14 @@ proc main(bam: hts.Bam, chrom: region_t, mapq: int, eflag: uint16, iflag: uint16
       else:
         var line = newStringOfCap(32)
         line.add(starget)
-        var start = newString(12)
-        var stop = newString(12)
-        var value = newString(8)
         for p in gen_depths(arr):
+          # re-use line each time.
           line.setLen(starget.len)
-          fastIntToStr(p.start.int32, start)
-          fastIntToStr(p.stop.int32, stop)
-          fastIntToStr(p.value.int32, value)
-          line.add(start); line.add('\t')
-          line.add(stop); line.add('\t'); line.add(value)
+          fastIntToStr(p.start.int32, line, line.len)
+          line.add('\t')
+          fastIntToStr(p.stop.int32, line, line.len)
+          line.add('\t')
+          fastIntToStr(p.value.int32, line, line.len)
           discard fbase.write_interval(line, target.name, p.start, p.stop)
     if quantize.len != 0:
       if tid == -2 and quantize[0] == 0: