1.8 can be found in the following code:
PlayerConnection.java
if ((d15 > SpigotConfig.movedWronglyThreshold) && (!this.player.isSleeping()) && (!this.player.playerInteractManager.isCreative()))

{ flag1 = true; c.warn(this.player.getName() + " moved wrongly!"); }

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if ((d15 - d14 > SpigotConfig.movedTooQuicklyThreshold) && (this.checkMovement) && ((!this.minecraftServer.T()) || (!this.minecraftServer.S().equals(this.player.getName()))))

{ c.warn(this.player.getName() + " moved too quickly! " + d11 + "," + d12 + "," + d13 + " (" + d11 + ", " + d12 + ", " + d13 + ")"); a(this.o, this.p, this.q, this.player.yaw, this.player.pitch); return; }

1.9：
PlayerConnection.java
if ((!this.player.K()) && (d11 > 0.0625D) && (!this.player.isSleeping()) && (!this.player.playerInteractManager.isCreative()) && (this.player.playerInteractManager.getGameMode() != WorldSettings.EnumGamemode.SPECTATOR))

{ flag1 = true; LOGGER.warn(this.player.getName() + " moved wrongly!"); }

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if ((!this.player.K()) && ((!this.player.x().getGameRules().getBoolean("disableElytraMovementCheck")) || (!this.player.cB())) && (
(!this.player.cB()) || (

(d11 - d10 > Math.pow(10.0F * i * speed, 2.0D)) && ((!this.minecraftServer.R()) || (!this.minecraftServer.Q().equals(this.player.getName()))))))

{ LOGGER.warn(this.player.getName() + " moved too quickly! " + d7 + "," + d8 + "," + d9); a(this.player.locX, this.player.locY, this.player.locZ, this.player.yaw, this.player.pitch); return; }