From 07ec93a7ef7d186885a88871a49fb5065895e913 Mon Sep 17 00:00:00 2001
From: Ryan Oldenburg <ryan@guzba.com>
Date: Thu, 12 May 2022 18:55:22 -0500
Subject: [PATCH] shrink overflow+range checks off to just idct

---
 src/pixie/fileformats/jpeg.nim | 32 ++++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/src/pixie/fileformats/jpeg.nim b/src/pixie/fileformats/jpeg.nim
index e9333bd..3689cbb 100644
--- a/src/pixie/fileformats/jpeg.nim
+++ b/src/pixie/fileformats/jpeg.nim
@@ -472,8 +472,6 @@ proc getBitsAsUnsignedInt(state: var DecoderState, n: int): int =
   state.bitCount -= n
   return k.int
 
-{.push overflowChecks: off, rangeChecks: off.}
-
 proc decodeRegularBlock(
   state: var DecoderState, component: int, data: var array[64, int16]
 ) =
@@ -489,7 +487,7 @@ proc decodeRegularBlock(
       state.getBitsAsSignedInt(t)
     dc = state.components[component].dcPred + diff
   state.components[component].dcPred = dc
-  data[0] = dc.int16
+  data[0] = cast[int16](dc)
 
   var i = 1
   while true:
@@ -506,7 +504,7 @@ proc decodeRegularBlock(
       if i notin 0 ..< 64:
         failInvalid()
       let zig = deZigZag[i]
-      data[zig] = state.getBitsAsSignedInt(s.int).int16
+      data[zig] = cast[int16](state.getBitsAsSignedInt(s.int))
       inc i
 
     if not(i < 64):
@@ -531,11 +529,11 @@ proc decodeProgressiveBlock(
     let
       dc = state.components[component].dcPred + diff
     state.components[component].dcPred = dc
-    data[0] = (dc * (1 shl state.successiveApproxLow)).int16
+    data[0] = cast[int16](dc * (1 shl state.successiveApproxLow))
 
   else:
     if getBit(state) != 0:
-      data[0] += (1 shl state.successiveApproxLow).int16
+      data[0] = cast[int16](data[0] + (1 shl state.successiveApproxLow))
 
 proc decodeProgressiveContinuationBlock(
   state: var DecoderState, component: int, data: var array[64, int16]
@@ -576,7 +574,7 @@ proc decodeProgressiveContinuationBlock(
         inc k
         if s >= 15:
           failInvalid()
-        data[zig] = (state.getBitsAsSignedInt(s.int) * (1 shl shift)).int16
+        data[zig] = cast[int16](state.getBitsAsSignedInt(s.int) * (1 shl shift))
 
       if not(k <= state.spectralEnd):
         break
@@ -592,9 +590,9 @@ proc decodeProgressiveContinuationBlock(
           if state.getBit() != 0:
             if (data[zig] and bit) == 0:
               if data[zig] > 0:
-                data[zig] += bit.int16
+                data[zig] = cast[int16](data[zig] + bit)
               else:
-                data[zig] -= bit.int16
+                data[zig] = cast[int16](data[zig] - bit)
     else:
       var k = state.spectralStart
       while true:
@@ -628,12 +626,12 @@ proc decodeProgressiveContinuationBlock(
             if getBit(state) != 0:
               if (data[zig] and bit) == 0:
                 if data[zig] > 0:
-                  data[zig] += bit.int16
+                  data[zig] = cast[int16](data[zig] + bit)
                 else:
-                  data[zig] -= bit.int16
+                  data[zig] = cast[int16](data[zig] - bit)
           else:
             if r == 0:
-              data[zig] = s.int16
+              data[zig] = cast[int16](s)
               break
             dec r
 
@@ -679,6 +677,8 @@ template idct1D(s0, s1, s2, s3, s4, s5, s6, s7: int32) =
   t1 += p2 + p4
   t0 += p1 + p3
 
+{.push overflowChecks: off, rangeChecks: off.}
+
 proc idctBlock(component: var Component, offset: int, data: array[64, int16]) =
   ## Inverse discrete cosine transform whole block.
   var values: array[64, int32]
@@ -755,6 +755,8 @@ proc idctBlock(component: var Component, offset: int, data: array[64, int16]) =
     component.channel.data[outPos + 3] = clampByte((x3 + t0) shr 17)
     component.channel.data[outPos + 4] = clampByte((x3 - t0) shr 17)
 
+{.pop.}
+
 proc decodeBlock(state: var DecoderState, comp, row, column: int) =
   ## Decodes a block.
   var data {.byaddr.} = state.components[comp].blocks[row][column]
@@ -819,9 +821,9 @@ proc quantizationAndIDCTPass(state: var DecoderState) =
 
         for i in 0 ..< 64:
           let qTableId = state.components[comp].quantizationTableId
-          if qTableId.int notin 0 ..< state.quantizationTables.len:
+          if qTableId.int >= state.quantizationTables.len:
             failInvalid()
-          data[i] = data[i] * state.quantizationTables[qTableId][i].int16
+          data[i] = cast[int16](data[i] * state.quantizationTables[qTableId][i].int32)
 
         state.components[comp].idctBlock(
           state.components[comp].widthStride * column * 8 + row * 8,
@@ -888,8 +890,6 @@ proc grayScaleToRgbx(gray: uint8): ColorRGBX =
   result.b = g
   result.a = 255
 
-{.pop.}
-
 proc buildImage(state: var DecoderState): Image =
   ## Takes a jpeg image object and builds a pixie Image from it.