diff --git a/src/gates/AmplitudeDisplay.js b/src/gates/AmplitudeDisplay.js
index cf89fb6a..a2faef91 100644
--- a/src/gates/AmplitudeDisplay.js
+++ b/src/gates/AmplitudeDisplay.js
@@ -182,7 +182,7 @@ const SPREAD_LENGTH_ACROSS_POLAR_KETS_SHADER = makePseudoShaderWithInputsAndOutp
     uniform float bit;
 
     float xorBit(float v) {
-        float b = mod(floor(v/bit), 2.0);
+        float b = floor(mod(floor(v/bit) + 0.5, 2.0));
         float d = 1.0 - 2.0*b;
         return v + bit*d;
     }
@@ -257,7 +257,7 @@ const TO_RATIOS_VS_REPRESENTATIVE_SHADER = makePseudoShaderWithInputsAndOutputAn
     ],
     Outputs.vec4(),
     `vec4 outputFor(float k) {
-        return vec4(read_ket(k), read_rep(mod(k, len_rep())).xy);
+        return vec4(read_ket(k), read_rep(floor(mod(k + 0.5, len_rep()))).xy);
     }`);
 
 /**
diff --git a/src/gates/ModularAdditionGates.js b/src/gates/ModularAdditionGates.js
index 18b84098..29248570 100644
--- a/src/gates/ModularAdditionGates.js
+++ b/src/gates/ModularAdditionGates.js
@@ -33,16 +33,8 @@ const MODULAR_ADDITION_SHADER = ketShaderPermute(
         }
         float d = read_input_A();
         d *= factor;
-        d = mod(d, r);
-        float result = mod(out_id + r - d, r);
-
-        // Despite sanity, I consistently get result=33 instead of result=0 when out_id=0, d=0, r=33.
-        // HACK: Fix it by hand.
-        if (result >= r) {
-            result -= r;
-        }
-
-        return result;
+        d = floor(mod(d + 0.5, r));
+        return floor(mod(out_id + r - d + 0.5, r));
     `);
 
 ModularAdditionGates.PlusAModRFamily = Gate.buildFamily(1, 16, (span, builder) => builder.
diff --git a/src/gates/MultiplyAccumulateGates.js b/src/gates/MultiplyAccumulateGates.js
index 933739b1..e5f7f2d0 100644
--- a/src/gates/MultiplyAccumulateGates.js
+++ b/src/gates/MultiplyAccumulateGates.js
@@ -44,10 +44,10 @@ const BIG_MUL_MOD_SHADER_CODE = `
         float t = 0.0;
         float r;
         for (int k = 0; k < ${Math.ceil(Config.MAX_WIRE_COUNT/MUL_STEP)}; k++) {
-            r = mod(f, ${1<<MUL_STEP}.0);
+            r = floor(mod(f + 0.5, ${1<<MUL_STEP}.0));
             f -= r;
-            t = mod(t + b*r, modulus);
-            b = mod(b * ${1<<MUL_STEP}.0, modulus);
+            t = floor(mod(t + b*r + 0.5, modulus));
+            b = floor(mod(b * ${1<<MUL_STEP}.0 + 0.5, modulus));
             f /= ${1<<MUL_STEP}.0;
         }
         return t;
diff --git a/test/webgl/ShaderCoders_Base.test.js b/test/webgl/ShaderCoders_Base.test.js
index b6ad48fc..fca8cb92 100644
--- a/test/webgl/ShaderCoders_Base.test.js
+++ b/test/webgl/ShaderCoders_Base.test.js
@@ -43,7 +43,7 @@ suite.testUsingWebGL("boolOutputs", () => {
     let output = BOOL_TYPE_CODER.outputPart;
     let shader = combinedShaderPartsWithCode([output], `
         bool outputFor(float k) {
-            return mod(k, 3.0) == 1.0;
+            return floor(mod(k + 0.5, 3.0)) == 1.0;
         }`);
 
     assertThat(shaderWithOutputPartAndArgs(shader, output, []).readBoolOutputs(3)).isEqualTo(new Uint8Array([